1.

A computer system consists of hardware and software.
The hardware is the physical part of the system. All computer systems require at least
four types of hardware.

INPUT

PROCESSOR

OUTPUT

STORAGE





An input device is any piece of hardware that allows data to be transmitted to the
computer processor. No computer, however powerful, is of value unless it is possible
to give it instructions and data to be used when those instructions are carried out.
An output device is any piece of hardware that allows the computer processor to
convey information or the results of its processing. There is no point in having a
computer system carrying out processing of any sort unless the results of that
processing can be either reported or used to effect future input to the system.
Storage is any piece of hardware which can store data outside the processor in a form
which is suitable for input back into the processor. This is necessary because data
must be saved for future use if the processor is switched off and for transfer from one
machine to another.

Descriptions of the basic hardware types will be given in Chapter 5.
The software of a computer system is the various sets of instructions which tell the
system how to do things. These sets of instructions are collected together in workable
groups known as programs. Without programs of instructions computers would not be
able to function because they would not know what to do.

1.1.1 Different Software Types
Sets of instructions to make a computer do something are grouped together as programs.
These programs make up the software of a computer system.
Depending on the sort of task that a program is expected to accomplish they are grouped
into different types of software.










Operating system software is a program, or set of programs, which control the
operation of the computer system. They are responsible for the way that the pieces of
hardware communicate with each other and for monitoring the way that the hardware
of the system is used.
User interface software is used to provide a method of communication between the
person using the system and the system itself. Put very simply it is what you see on
the screen when you are using the computer.
Translator software is necessary because the computer uses a language that is difficult
for human beings to understand and a computer is not capable of understanding
human language. The translator software provides the computer with the equivalent
of a Chinese-English dictionary so that it can look up what things mean.
Utilities, or utility programs, are system programs designed to carry out common
tasks; for instance the programs that control output to the printer or the storage of
data.
Programming languages are used to write sets of instructions that the processor can
understand because it has a translator for that language. There are many different
programming languages, each of which has been designed for a particular type of
problem.
Common applications software includes word processors, graphics, spreadsheets, and
many others. These are the programs that you use to produce something worthwhile
on the computer.

All of these different software types will be covered in more detail later on in the work.
For the moment, the important thing is that you understand that there are different types
of software designed to carry out different tasks, and that you can give a brief description
of each.

Systems Software and Applications Packages
Systems Software.
Computers are machines that can carry out operations very quickly. This does not mean
that they are in any way intelligent. However fast the machine can work, it is useless if it
does not know what to do. Computers need specific instructions for even the most trivial
of tasks. If a computer user had to supply these instructions there would be very few
people able to use one. Consequently, the manufacturer of the machine will provide
programs that are accessible to the user by using very simple commands, these programs
are the system software.
 The operating system is the set of programs that control how the computer responds
to user requests. Examples that you may have used include DOS and Windows.
 Utility programs are additional routines that can be added to an operating system or
that are available to the user within an operating system. An example that you may
have on your computer system would be a piece of back-up software that can be used
to make sure that you do not lose all your work when the computer fails.
 Some frequently used routines are stored in such a way that they are accessible to
users. These routines are stored together in a system library, and form part of the
system software. This is something of a grey area between system software and
application software because application software also gives access to library areas.
 Program translators are needed in order to allow users to produce programs in a
simple format which can then be translated into something which the computer will
understand.
Applications Packages.
A piece of applications software is a program, or set of instructions, designed to make the
computer carry out some task. It differs from system software in that it makes the
computer do something that is useful for the user. Word word-processing software, or
Paintbrush graphics software are both examples of applications software because they
both allow the user to produce something that is of general use.
If the software can be used in many different situations to accomplish different things
then it is said to be generic software. For example a word processor can be used to write a
letter, or to produce a report, or type an essay,… A word processor is a piece of generic
software.
If the software contains programs that allow lots of different tasks to be carried out,
together with a book of instructions telling the user how the software should be used, then
it is called an Applications Package.
An integrated package consists of several parts, each of which is an application package.
Further, the integrated package is designed so that users can easily move data between the
different parts of the integrated package. For example, if two of the parts are a wordprocessor and a drawing package, users can move a drawing, created using the drawing
package, into the word processing package.

is an off-line system. it
is also possible to change it by altering the programs that are being used to control it. a bank’s computer
system is used a lot during the day-time by bank employees.
. we will
content ourselves with a brief look at four different groups of system software.
The fundamental principle behind batch processing is that there are some jobs that need
to be done on a computer that take lots of time to do and stop the computer doing other
things. you would expect the computer to take account of the fact that you just
turned right before it decides the next position of your car.
3. but at night time it is used
very little.
Just as it is possible to change a computer system by buying a new piece of hardware.
Off-line processing is when the user (or input) does not have direct contact to the
processor.
A real-time system must be on-line because otherwise the input would not be able to
reach the processor fast enough to affect the output. Big jobs that can be made to wait are put together in a “batch” which are all dealt
with when the computer is not needed for anything else. at the different effects that it is possible to get by
changing the operating system software at a later stage in this course.1. If the computer was not in real
time mode. On-line processing. if you are playing a computer game where you are driving a car
around a course. If you are
reading this on a stand alone computer then you are probably on-line because your
commands are being dealt with by the computer system as soon as you input them. The bank statements that take a long time to print out are collected together
and sent through the system at night time when the computer is free. your decisions would come too late to affect the game. in some detail. For instance.
A real-time processing system is one which makes decisions quickly enough to effect the
next input. Batch processing.
We will be looking. For instance. For now.
1.
2. Off-line processing.d Modes of Computer System Use
An operating system is a set of software that controls the working of a computer system. This
is as opposed to…
4. Real-time processing. A system where input at a keyboard
is stored on a disk before being input to the processor later.
On-line processing is when the user has direct contact with the processor.1.

Most operating systems comprise a large set of programs.
When you are using an applications package you are not communicating with the
computer hardware.S.1 Operating Systems
An operating system is a set of programs designed to run in the background on a
computer system. the computer is useless. giving an environment in which application software can be executed.2 System Software
1.
Operating system
User
Programmer
Hardware
Applications
package
. The
operating system sits between the hardware and the application program or user. only some of which are stored
in the processor memory all the time. This not only saves
space in the processor memory but also means that the O. you are communicating with the operating system. can be easily changed to a
different one. are
stored on the hard drive so that they can be accessed when required. no matter how many programs you have. Many of the routines available in the O.1.2.S. Without an
operating system.

There are two simple solutions to this problem.
telephone) bills from customer records. Lots of programs that need
to be run are collected together (to form a batch) and they are sent to the computer. The big problem was
the ‘speed mismatch’ between the user sitting at the keyboard who was very slow. Most real-time systems are based on control of some process in the real
world or on information handling.2. production of gas (electricity. it would not be sensible for the
computer to be running any O. one is to
buy more machines and the other is to make the machines work more effectively by
taking away the slowest part of the system – the human being. the compilation of high level language programs
where a number of users want programs compiled.S.S. and the
machine which was very fast. When it finds the correct code it can
report to the user the number of that item that there are in the store.
 the data is very similar in nature and…
 it requires similar processing. In this example.
Typical examples of applications which would be done using batch processing include
production of bank statements from customer files.1 Types of Operating System
Batch Processing:
When computing was still a new science. A
robot trolley is controlled by a processor which takes input from a sensor following a
black line on the floor. it might mean that the reaction is corrupted in some way. The temperature is monitored by a
computer which accepts input from a sensor and then makes a decision whether to adjust
the heating elements in the vessel. This problem gave rise to the
development of batch processing. is one which can react quickly enough to affect the next input.
 the computer system has identifiable times when it is not being used. the trolley would very
soon leave the black line because it would not be steering quickly enough.1. or process
to be carried out. Nowadays we might well
opt to buy more machines. batch processing tends to be used where
 there are large amounts of data to be processed.. and so has
available processor time
 the application does not require human intervention.S. there were not enough machines to satisfy the
demand for processor time from students in universities who wanted great calculations
done. it would be necessary to record the fact that a shopper had bought it
. If the processor was not controlled by a real-time O. The
batch operating system then controls their passage through the computer. and many others.
Real-time:
A real-time O. A catalogue
shop processes orders by the code for a product being input and the system then
comparing the code with information in its files. but this used not to be an option.
A batch processing operating system is one that does not allow for interaction between
the user and the processor during the execution of the work. that is not real-time because if there was a delay in the
decision making process. If there was only one
left of a certain item.
Nowadays. firms who wanted their payroll worked out. and makes decisions concerning steering to keep the trolley on the
black line. A chemical plant has a reaction vessel where the
temperature is critical to the result of the process.

but we shall return to this in a later chapter. at any one time. It appears that more than one task is running
simultaneously. A perfect example of a
single user system is the one that you may have at home. Again. this machine is called the server. that most of us use on our
own computer systems. Real-time systems tend to display a high rate of redundancy. These terminals are not computers as in the case of the
network system. An ordinary network will have a server controlling it and the access to the hard
drive. and so can be kept up to date relatively easily. Windows. as the name implies.S. This means
that it cannot be using up some of its slack time doing other tasks while it is waiting to be
asked to do something.S. Only one person uses it at a
time. which is connected to the server. and their programs.
Distributed:
A distributed system is one that allows software and data files to be distributed around a
system.
Multi-user:
Again. On a
simple single user system you will probably be used to having a number of things
running at the same time. Perhaps one window shows a spreadsheet while another shows
a word processing application. A time-sharing system has a single (normally powerful) computer which is connected
up to a number of terminals. such a
system allows communication between users on the system and also allows sharing of
hardware and software across the system. they just appear to be. while the files of work are stored
somewhere else. that allows several applications to be available simultaneously.S.
At the moment it is difficult to tell the difference between the two types of multi-user
system. This implies that the computer will not be using its full potential
as far as processing is concerned. Networks are important
because they allow hardware and software to be shared and also mean that a single copy
of the information on a system is needed. Normally one of the machines is used to
control the rest of the system.S.before the next shopper has their request dealt with otherwise the second person might be
sold the same item.
2.
There are two types of multi-user O. This can
.S. a single user O. but have a very limited amount of processing power. Most single user systems are also
Multi-tasking:
This is a type of O.S. services more than one user simultaneously. and the spreadsheet software is stored on a third disk drive. The O.:
1. needs to be ready to handle input as soon as it comes in. Because the information on the system must be processed
immediately the O. is specifically one that is used to control a system
which has only one user.
Single User:
As the term implies. is a multi-tasking O.S. When this happens it is said to display a high rate of
redundancy. this type of O. They aren’t. You may decide to copy the sheet from the spreadsheet
software to the word-processed document. A distributed system might store the word
processing software on one computer’s hard drive. A network system comprises a number of computers linked together for the purposes
of communication and sharing of resources.

.speed access to files because there is no single bottle neck which all the information must
pass through.

). shopping. The first screen may ask
for the general area of interest (accommodation.
Form based
If the majority of the input to a system is of a standard type.1.
The characteristics of a form based interface are that
 it has specified areas for the data. Examples of this would be information systems for
tourists or users of a particular service.
Imagine a system at a train station in a popular holiday location.. There are different types of interface. and so on until the result is obtained. entertainment. and areas to be filled in with textual information
 it has a cursor which moves to the next box to be filled in. trips. A list of choices is made available followed by a
further set of choices based on the first choice. once
the choice of accommodation has been made the next screen may offer different
standards of hotels. For example. and finally a list of
all the available properties that match the previous choices. The
means of communication between the user and the machine is known as the user interface
and consists of both hardware and software. The person also receives responses from the computer.
Menu based
Menu based interfaces are used in situations where the operator tends not to know what
the options are that are available. The next screen may offer different price bands. This sort of interface would be used where an operator is inputting
information while asking a customer questions over the telephone. sometimes the box is
highlighted to make it clear to the operator where the data is to be inserted
 some of the boxes are more important than others and the cursor will not move on
until some data has been supplied
 it checks that what has been input is sensible for that box before moving on to the
next. The interface
 prompts the operator to ask all the questions
 makes the operator input the information in the correct order
 ensures that the information is input in the correct format by having specific areas to
input the data
 makes the checking of the information easier.
Graphical
.
Input is often done using a touch screen because of the location of such systems and
because the people who use them are often in no way computer literate.2. then a typical interface will produce a form on the
screen to be filled in. in other words the computer
knows what sort of input to expect. meaning that
simple systems are essential.2 Types of User Interface
A computer is used by a person who needs to communicate with the machine in order to
instruct it as to their wishes. boxes for input of coded material like
the date or the sex of the customer. which
are useful in different situations and for different types of user.

icons. and also needs to understand the way files are stored on the
system. The trick is that the system restricts itself to questions to which the only
sensible answers are the ones that it knows. particular how information is
stored. First. but the user would expect to be able to view different applications or files
on the screen.
This can be particularly important for the system manager because different users can
only be allowed to have access to specific parts of the system. The user needs to know what
the possible commands are. this is done by putting each into its own boarded area known as a window.
1. The second characteristic
is that command based interfaces can only be used by computer literate people because
you not only have to understand the commands and their uses but you also need to
understand something about how the computer operates.
menus. These points will be made when the appropriate stage is reached
in this course.
There are many other points to be made about interfaces.
. hardware drivers. file compression and virus checkers. a
message is produced which makes clear that a further attempt is required. The terms describe what the user sees on the screen. especially the fact that the
second part of the interface consists of the hardware necessary to put the software
interface into operation. typically this would be a
mouse. the computer will ask questions
which elicit a response which gives the user the impression that they are talking to the
computer. file handling. Other interfaces restrict the options that the user has available to them.
Natural language
Sometimes referred to as a conversational interface.Graphical interfaces are called GUI (graphical user interface) or WIMP (windows.
Command line
Or command based interface is one where the user types a series of commands at the
keyboard which tell the computer what their intentions are. An example that you may have on
your computer system would be a piece of back-up software that can be used to make
sure that you do not lose all your work when the computer fails. The characteristics of a command based interface are
 the user needs to know what commands are available
 the user needs to understand the commands
 the user needs to understand the way that material is stored in the computer system
Because of the above points there are two very important characteristics about a
command based interface. pointer).3 Utility Software
Utility programs are additional routines that can be added to an operating system or that
are available to the user within an operating system.
The user will expect to be able to select options by use of menus of choices and by using
small pictures which represent the different options available. There are many
different types. If the user leaves the expected responses. the system is very much more open than in the other
types of interface.2. Others are disk
formatting. Choices are selected by the
user by using some sort of pointing device to indicate choice.

-In order to store files which are too large to be stored in the processor itself.
1.Example Questions. Notice that there are more than two acceptable
answers.
In this example there would be no mark for saying that software are the other parts
that are not physical. Note that there are
two indicators in the question that you should give two answers.. but never give more than one extra answer because you then demonstrate that
you are not sure and the examiner will choose your first two answers. -System software controls how the computer system works while…
-application software allows the user to make the computer do something useful.
-software are the programs that make the machine produce useful results.
3. -In order to store files when the power to the processor is switched off.
Explain the difference between hardware and software. This was
expected because of the use of the words explain the difference in the question. This question does not ask for a comparison or an
explanation.
Again. the word in bold
and the number of marks.
There are two marks available for the question so make sure that you have said two
distinct things. so don’t give them. while. If you can think of three then give them. Make sure that the second point is not just the opposite of the first.
NOT for what is stored.
-To allow for the transfer of data from one machine to another. this is a comparison type of question so the two parts of the answer should
be related.
2. Be careful to answer the question asked.
Describe the difference between system software and application software.
Notice that the answer suggested provides a link between the two terms. right or
wrong.
Notice that the question asks for reasons why the system needs to have storage.
Give two reasons why a computer system would need to have some type of external
storage device. -Hardware comprises the physical parts of the computer system. until
they are needed. the examiner will choose the two
best.
(2)
A.
(2)
A.
.
(2)
A.

leaves very little room for
manoeuvre because it is asking for a standard answer.
Give an example of a computer application which would use
(i) batch processing. Note. some of the marks are always reserved for the last part of the
question. Always try to give one more
answer than seems to be required by the question. An integrated applications package contains
-a number of different pieces of software which…
-can communicate with each other in order to…
-allow the user to produce valuable work. the fact that three answers have been given.
(ii) real-time processing
and give a reason why each of your suggestions is appropriate.
Generic software is
-software that can be used in many areas for different end products.
An integrated applications package contains a number of different pieces of generic
software.
If you look at a mark scheme for an examination paper. the mark points are listed as
a set of bullet points so there is no reason why you should not do the same. Also.
State what is meant by an integrated applications package and generic software.4. This is not an opportunity to
show your prowess by making up an answer that is original.
A question which begins with the word define.
(4)
A. while initiative
is applauded.*
6
Define what is meant by the term operating system.
(ii)-Playing a computer game because…
-you expect that any decision that you might make should be dealt with before the
computer makes its next move. (i) -Printing bank statements for all the bank’s customers…
-can be done at a time when other work is not being done. The
warning is always “Don’t throw marks away”.
5. this
does not mean that all three marks can be gained by only answering one part. In this
type of question. Some
students decide to come up with something new in questions like this and. often don't explain their application well enough to get the mark.
(3)
A.
(2)
A.
*Notice that it is important to make a conscious decision about how the marks will
probably be awarded to stop you wasting time giving more thorough answers than
necessary.
Notice the fact that there are three mark points for the first part of the answer. there are certain standard answers that will always be right. This
style of answer helps you to write down your thoughts easily without getting
.
also. -A (suite of) programs…
-which run the basic functions of the computer…
-giving an environment in which to run application software.there aren’t any.

S.
7. the first
time that you use the term operating system write “…operating system (OS)…”
you can then use OS as often as you like in the rest of your answer.
(2)
A. . If you do need to use an
abbreviation. where the abbreviation is the accepted form. even. .Storage of the operating system on backing storage allows for easy upgrading or
changing from one system to a different one.
. It is
important when answering a question starting with ‘distinguish’ to choose facts that
show a comparison. has been resisted in
the answer.
Note that the temptation to call the operating system the O. In general. but most of them would not answer the question. but your own versions may
be ambiguous or.
8
Distinguish between a multi-tasking and a multi-access operating system.
(2)
A. give the term in full
with the abbreviation that you want to use in brackets after it. For example.confused by the language. The purpose of this examination is not to test your ability
with English. not understood by the examiner.A multi-tasking operating system is one where the user of the machine is given the
impression that they can carry out more than one task at a time. rather to test your knowledge of computing.
.A full operating system requires a large amount of storage space that is better
utilised in the computer memory for applications
. because the term is to be used a number of times.
Give two reasons why an operating system is likely to be stored on backing storage
rather than in the memory of the computer. There are
exceptions.
Note that there are a large number of points that could have been made about both
of these operating systems.A multi-access operating system is one where it is possible for more than one user
to access the system apparently at the same time. do not use abbreviations in your answers.

either explicitly
or implicitly.(2)
A. so that the computer can check the file and
determine whether there are any of that item available.
b)Advantages:
-Entire system is available to the technician
-Access to the particular part of the system required is gained more quickly than
using other types of interface. are not only going to score no marks. The language used in this answer is not the sort of language that a candidate
will use in an examination.
.
.
What is just as important here are the things that would not be on the screen.
(3)
A.
11
The technician responsible for maintaining the system in question 5. Answers like “so that you can
get around the system” are perfectly acceptable.
(2)
b) Give two advantages and one disadvantage to the technician of using a command
line interface rather than a menu based interface. . but will
probably be penalised because they demonstrate that the candidate has not
understood the question.9
State what is meant by a distributed system. with what the comparison should be made. or method of payment. and give an advantage of this type of
multi-access system over a simple network of machines. In this type of question it is important to demonstrate that
you have taken the situation into account.
Note. Be careful to give an
advantage using this comparison and not a more generalised one.Access to files can be speeded up because more than one file command can be
carried out at a time. uses a
command line interface. The
question makes it quite clear that there is no ordering going on. a)-Series of commands typed at a screen prompt…
-which give specific instructions to the computer.Catalogue number
.
a) Explain what is meant by a command line interface.Laid out with spaces for input.
(4)
A. Design a screen interface
that would be suitable for the operator to use.Space for the description of goods which will be filled in by the computer itself
.Form type interface
. so spaces for name
and address. Don’t worry about this.Spaces for computer to produce availability and price
. .A distributed system is one which uses many storage locations on different
machines to store software and files. The operator needs to type in a series of
responses to questions put to the caller.
10
A computer operator takes phone calls from the public who ring up asking whether
a particular item in a catalogue is available.
Disadvantage:
-The technician needs to know the commands that are available
-The technician needs to understand the way the system is designed so that it can be
navigated efficiently.
When an advantage is asked for it is normal to state in the question.

If electricity is
not flowing through a wire that can stand for 0.
Counting is one of the first skills that a young child masters. This is very difficult to learn because of all the symbols
needed. and none of us consider
counting from 1 to 100 difficult. so we can
count on our fingers until we get to the last one. Structure and Management
1. which we remember in the next column
and then start again. what we need is a carry system. 6 * 60 degrees = 1 revolution.2…9 and also to understand that two identical symbols
mean totally different things according to their ‘place’ in the number. We can’t just pump through twice as
much electricity. in 23
the 2 actually means 2 * 10.
. which makes the system more
difficult. For instance.
A computer is an electronic machine.3 Data: Its Representation. the
meanings of the symbols 0.3 Number Systems and Character Sets. we have to learn.
We don’t need to count in tens. But why multiply by 10? Why not multiply by 6? The
answer is simply that we were taught to do that because we have 10 fingers. If electricity is flowing. just like what happens when we run out
of fingers. Electricity can be either on or off. What we need is another wire. then it stands for
1.1. The ancient Babylonians counted in a system. The difficulty is what to do for the number 2. it seems reasonable that if we decrease the number of symbols the system will
be easier to use. 60 seconds
= 1 minute.1. to count. which is
similar to counting in sixties. However. but we still use a system based on sixties today: 60 minutes = 1 hour.
Instead of increasing the number of symbols in a system. by heart.

A single bit has very few uses so they are grouped
together.
These are stored as codes which look like binary numbers. is one bit.
Each wire. A group of bits is called a BYTE.
So each digit. Usually a byte has 8 bits in it. and what about the lower case letters
and punctuation and…? The computer can store as many characters as necessary simply
by using more and more bits for the code.The ‘units’ wire
no electricity
0
The ‘twos’ wire
no electricity
0
electricity
1
=0
ADD 1
=1
no electricity
0
no electricity
0
ADD 1
=2
Carry
electricity
1
electricity
1
electricity
1
no electricity
0
no electricity
0
electricity
1
ADD 1
=3
ADD 1
Carry
Carry
=4
The computer can continue like this for ever. For instance A could be stored
as 000. where there are only two digits. is known as the binary system. there are only 8 possible codes using 3 bits. or digit.
This system. The number of
. so
we could store the letters A to H but not the rest. 0 and 1. B as 001 and so on. is known as a binary digit. This name is normally shortened to BIT. Some systems don’t need to be able to
recognise a lot of characters so they only use a few bits for each character. just adding more wires when it gets bigger
numbers. 0 or 1.
One type of data that needs to be stored in computer systems is the letters of the alphabet. Unfortunately.

Most systems use ASCII
so you can be fairly sure that when you type in A it is stored in the computer’s memory as
01000001. so how can it tell the difference?
The answer is that characters and numbers are stored in different parts of the memory. If my computer stores A as
01000001 and your computer stores A as 01000010 then the computers cannot
communicate because they cannot understand each other’s codes. (This is not quite true. This standard set of codes is known as the ASCII set. you can’t be certain because some systems use other codes.)
A problem arises when the computer retrieves a piece of data from its memory. we will see why in chapter 1.
ASCII uses 8 bits so there are 256 different codes that can be used and hence 256
different characters.bits needed to store one character is called a byte which is usually said to have 8 bits
because most systems use 8 bits to store the code for each character. A less
common code is called EBCDIC.6.
We now have enough codes. but another problem arises. Is this the number 65. so
it knows which one it is by knowing whereabouts it was stored. However. it was developed for use by larger scale computer
systems and differs in that the code for each character is different than that used in ASCII.
Notes: All the characters that a system can recognise are called its character set. Imagine
that the data is 01000001. or is it A?
They are both stored in the same way.
. In the 1960’s a meeting
in America agreed a standard set of codes so that computers could communicate with
each other.

Numeric data. Data which can only have two
states like this is known as BOOLEAN data. and then a separate part is the number of places the point has had to
move to get it to the front. A simple check of that value would tell the processor whether it was safe to
fill the machine with water. Simply remember that fractions are stored in binary with the
point at the front.
Numbers can be restricted to whole numbers. then.23 so we need an extra piece of data to be stored. Because the first stage is always to move the point to the front of the number.3 and . but that is more than enough
for this part of the course.
A simple example of its use would be in the control program for an automatic washing
machine.
There are different types of numbers that the computer must be able to recognise. All of
these different types of data will look the same because they all have to be stored as
binary numbers.1.23
will now both be stored as . The computer can distinguish one type of data from another by seeing
whereabouts in memory it is stored. It is usual to use
either 2 bytes (called short integers) or 4 bytes (called long integers).
Another type of number is a fraction (or decimal). The computer uses binary data which consists of bits of information that can be
either 0 or 1. These special forms of data can be set up by the computer system
so that they are recognised when entered. There are only two
options. A boolean variable could be set to 0 if it was open and to 1 if
it was shut.
and it is like the point “floating to the top”. Fractions. However. Obviously there is a lot missing from this explanation. the difference being
simply that long integers can store larger numbers.3. Two examples of such data types are Date/Time
and Currency. these are called INTEGERS and are stored
by the computer as binary numbers using a whole number of bytes. these have to be treated as different types of data by the computer
because the Most Significant Bit (MSB) of the data stands for something different than in
an ordinary unsigned integer. true or false.
Some types of data are used so often by computer systems that they are considered to be
special forms of data. fractions are stored in FLOATING POINT
form. 2. are stored in two parts: the fraction
part (called the mantissa) and the number of places the point has had to move (called the
exponent). Sometimes it is necessary to store
negative integers.
Boolean data
Sometimes the answer to a question is either yes or no. so it seems reasonable that the answer to such questions can be stored as a
single bit with 1 standing for true and 0 standing for false. Students will probably be familiar
.1 Data Types
The computer needs to use different types of data in the operation of the system. The computer has simply been told the rules that govern such data types
and then checks the data that is input against the rules. This is stored by changing the position
of the point so that it is always at the front of the number and then storing the fraction
that is left (there is no whole part because the point comes first). One of the important pieces of information for the processor would be to know
whether the door was shut. the number
of places the point has had to move.

with these data types through their use in databases. which is represented in the character set of the computer by
a character code in a single byte. Such data types are fundamentally
different from the others mentioned here because the others are characterised by the
operating system while these two are set up by applications software.
Characters
A character can be anything.
.

in
itself. Iram. this doesn’t let me identify individual names.
The array that has been described so far is really only a list of single data items. Initialising should be done before anything else so that
the computer knows what is coming. but don’t worry as use of multi-dimensional
arrays is for later in the course. Rashid.
perhaps their name. Sahin.g. the second. otherwise there may not be enough space left when
you want to use it. Lists like this
are called ARRAYS. Obviously
everything gets more complicated now. The first. might be stored in
location NAME.
. and certainly 20 different
variable names that made sense will be very taxing to come up with.2 Arrays
Data stored in a computer is stored at any location in memory that the computer decides
to use.1.
Initialising consists of telling the computer
 what sort of data is going to be stored in the array so that the computer knows what
part of memory it will have to be stored in
 how many items of data are going to be stored. this is called a two dimensional array. so that it knows how much space to
reserve
 the name of the array so that it can find it again. it is
important to tell the computer about it before it does anything else so that it can reserve
that amount of space in its memory. This. it is obvious that they are all
peoples’ names and that they are distinguishable by their position in the list.3.
Different programming languages have different commands for doing this but they all do
the same sort of thing. The array would now have 20 students and
more than one thing about each. but I’m now struggling. If it is necessary to store the 20 names of students in a group then each location
would have to be given a different variable name.
e. a typical command would be
DIM NAME$(20)
DIM is a command telling the computer that an array is going to be used
NAME is the name of the array
$ tells the computer that the data is going to be characters
(20) tells it that there are going to be up to 20 pieces of data.
Notes: Just because the computer was told 20 does not mean that we have to fill the array. This means that similar pieces of data can be scattered all over memory.
Because the computer is being forced to store all the data in an array together. the variable names are all going to have to be remembered. address. might be stored in FORENAME. Apart from anything
else. so if I call
the first one NAME(1) and the second NAME(2) and so on. It would
be far more useful if each student had a number of pieces of information about them. date of birth. doesn’t matter to the user.
could be stored in CHRINAME.
the 20 simply tells the computer the maximum size at any one time. This warning of the computer that an array is going to be used is
called INITIALISING the array. the third. However. except that to find each piece of data it has to be referred
to by a variable name.
Far more sensible would be to force the computer to store them all together using the
variable name NAME.

Else Add 1 to Counter
Endwhile
Print “Name not in array”
Try to follow the logic of the steps above. NAME$(11) = Rashid will place Rashid in position 11 in the array
(incidentally.
Searching for a particular person in the array involves a simple loop and a question
e.g.g. tell the computer which position in the
array and assign the data to another value
e. RESULT = NAME$(2) will place Sahin into a variable called RESULT.
To read data from the array is equally simple. erasing any other data that happened to be in there first.We should now have a picture of a part of memory which has been reserved for the array
NAME$
NAME$
Iram
Sahin
Zaid
Name$(1)
Name$(2)
Name$(20)
To read data into the array simply tell the computer what the data is and tell it the position
to place it in e. Do
If NAME$(Counter) = Liu Then Print “Found” and End.
.g. search for Liu in the array NAME$
Answer:
Counter = 1
While Counter is less than 21.

the last one of which has to be
one that cannot possibly exist so that the computer knows it has reached the end of the
list.
Imagine the list of names used in the example for the array. and the address of the first data in the list is stored separately. There are two major problems with arrays. Each of the locations that can hold
data are given an address. say size 50.
This tells the computer where the first piece of data is.1.
Linked lists are often drawn showing the data in boxes and the linking addresses as
pointers. Notice that the two problems associated with arrays no longer exist. In order to get the data back. This is the better method for describing a list. This is because the array size has to be predetermined. The
array could be made much bigger. These addresses are called pointers. the twenty people in the set could all be found by the one reference to NAME
which pointed to the location of the array. just don’t lose sight of the fact
that the arrows are really address references. the idea is simple if we look at it in diagram form.
Start address
61
Address
60
61
62
63
85
86
-
Data
Rashid
Iram
Next address
75
86
Zaid
XX
Sahin
60
The diagram is intended to show a portion of memory.2 Linked Lists
When data is stored in a computer the processor can store it in any location provided it
can get the data back. the computer goes to the next piece of data by using the address that is
stored with the data. If everything has to be in the index then the
index can get very large. One method for doing this is by using an
array. The
first is that if the size of the set grows because a new student joins there is no room in the
array to store the information. that most of this space will never be used. it seems reasonable to try to cut down the size of the index by
grouping things together under one index entry.3. so that we are sure it will never be too
small.
That sounds very complex. but this leads to the second problem. If the first data item is not the one
that is wanted. These problems can be overcome by using a
linked list.
consequently wasting valuable memory. each of the locations where the data is
stored is given an address so that if the computer can remember the address of where it
put some information it can easily retrieve it.
.
A linked list of data items tells the computer to store the data in any location and to link it
to the previous data item by giving the previous data item the address of the new one.

Follow the pointer to the next item
3. to remove Sahin from the example
Start
Iram
Sahin
Rashid
Zaid XX
Note that Sahin’s data is still there. all that needs to be done is to create a new start pointer for this list and
add it to the index of start pointers for all the other lists. If the pointer shows that the end of the list has been reached.
. report that it is found and end.Start
Iram
Sahin
Rashid
Zaid XX
Note: The jagged line signifies that there are a number of others which would fit in there.
To remove a value from a list.
but they are not shown. its just that there is no way of getting to it so it might
just as well not be.g.
4.
5. report that the item is not
there and end.
To search through the list for a particular piece of data follow these rules
1. If the item is the one being searched for. E. simply change the pointer that points to it into one that
points to the next value after it.
To initialise a list. Go to step 2. Find the correct list in the index of lists
2.

Iram.
2. Notice that the pointer is pointing to the next space.
Sahin. Iram’s job is input and goes as the next in the queue. These jobs are
held. Imagine Zaid. This seems to be wrong. Zaid is in the queue for printing. It is found by the computer at the space under the
pointer (Iram’s job). Zaid and Iram are in the stack.
3. Zaid’s job goes for printing so the start pointer moves to the next job.
Notes: The array is limited in size. the end pointer is pointing at where the next job will
go.
This would solve the problem of running out of space for the queue.
EP
EP
EP
SP
Zaid
1.
A stack will only need one pointer because adding things to it and taking things off it are
only done at one end
1. in that order. All the computer needs is a pointer showing it which
one is next to be done (start pointer(SP)) and another pointer showing where the next job
to come along will be put (end pointer(EP))
1. but does not feature
in this course until the second year.
.
SP
Sahin
Iram
3. It is only fair that when a job is called for by
the printer that Zaid’s job is sent first because his has been waiting longest.
Stacks. A job has been taken off the stack. The queue does not have to be held in an array. or
alphabetic. Sooner or later the queue will reach the end of the
array. it could be stored in a linked list.1. in an array.3. Sahin’s job has been placed on the stack in the position signified by the pointer. also Sahin’s job
has been input so the end pointer has to move.2 Stacks and Queues
Queues.
3. the end pointer moves to the next
available space. This type of unfair queue is called a stack. it may not be numeric. but there is an order dependent on the time that it arrives. The jobs are put in at
one end and taken out of the other. just like the other data we have been talking about.
SP
Iram
Zaid
2. the
pointer then moves up one.
2. Rashid send jobs for printing.
This would be a grossly unfair queue because the first one there would be the last one
dealt with.
Information arrives at a computer in a particular order. and the pointer moves down one. but there are reasons for this being
appropriate in some circumstances which we will see later in the course.
Imagine a queue where the data was taken off the array at the same end that it was put on. and the effect of this seems to be that the contents of
the array are gradually moving up. When these jobs arrive they are put in
a queue awaiting their turn to be dealt with.

Pointer
Pointer
Iram
Zaid
1.
. the Last one In is the First one Out.
In a stack. the Last one to come In is the Last one to come Out.
Sahin
Zaid
3.
In a queue. or FIFO (First in is the first out). or FILO
(First in is the last out). This gives the acronym LIFO.
Pointer
Zaid
2. This gives the acronym
LILO.

This information refers to a particular
student.
Data stored in computers is normally connected in some way.
. For example. address and so
on. for example “Iram Dahar”.
Because of this quality. If Iram
Dahar’s brother Bilal is in this set he will presumably have the same address as Iram. The data that goes in a field is called an ITEM of data. name. It might waste some space. telephone number. and it can only do this if it
can be sure that one of the fields will always contain different data in all the records. Sometimes a lot of space is
wasted and sometimes data has to be abbreviated to make it fit. “3671 Jaipur.
The data that goes into each field. that particular field in the record is different from all the others
and is known as the KEY FIELD. but the searching for
information can be done more quickly. Items.3.
Each student has their own information stored. it is called their RECORD of information. Fields. Each type of information is called a FIELD. For
example. 2415” will be
different in most of the records.
Note: Some fields may contain the same items of data in more than one record. address. The key field is unique and is used to identify the
record.
Each record of information contains the same type of information. A number of records make up a file. but it seems sensible that each person will have the same information
stored about them. Pervais Durrani is 15 characters. the data about
the 20 students in the set that has been the example over the last three sections has a
connection because it all refers to the same set of people. there may be two people in the set who happen to be called Iram Dahar.
Note: Iram Dahar is 10 characters (1 for the space). The alternative is to be
able to change the field size in every record. this
large quantity of data is called a FILE. A number of fields make up a record and
all records from the same file must contain the same fields. for instance their name. Records. It
makes it easier for the computer to store things if the same amount of space is allocated
to the name field in each record. When each of the records is assigned a certain
amount of space the records are said to be FIXED LENGTH.1. It is
important that the computer can identify individual records. this comes later in the course. Each person will have their own
information stored. In our example the records would contain a field called school number which
would be different for each student. exam grades…
All the information stored has an identity because it is all about the set of students.3 Files.

In other words there is no single right answer. why make life more complicated than necessary. in Britain. As we are not going to do any
arithmetic with these numbers. the school number (to act as the key field).
The amount paid is listed as an integer as the teacher will store the number of whole
dollars so far paid. A teacher is taking 50 students on a rock-climbing trip. This is not necessarily the best data type.
3 characters were allowed for form. give an example of what you mean by the
data.3 Record Formats. but you would have to say this in your answer. As you get to learn about other data types you may well be able to consider
better ones still. because of the nature of the exercise.3RJ)
Character
3 bytes
Notes: It would be perfectly reasonable to say that the school number was not a proper
number so it should be stored as characters (probably 4 bytes). There are other fields that could be
included but we will add just one more. If in doubt. 15 bytes would be perfectly reasonable.
The student name is quite arbitrary. remember
these are fixed length records.g. as would 25
bytes. but phone
numbers.
The fields necessary will be Student name.
To design a record format.1.
Answer. in this example currency
may be better.3.
. and integers are not allowed to. the computer can be programmed to put the 0 in at the start of the rest of the
number.
Many students expect that the emergency number should be an integer. their parents may need
to be contacted if there is an accident. start with a 0. Design the record format for the file. but there are
wrong ones.g. The students are being
charged 20 dollars each and. it can’t hurt and it may save you a mark in the question.
For each one of these fields it is necessary to decide what type of data they will be and
also to decide how many characters will be allowed for the data in that field. Amount paid. the first thing to do is to decide what information would be
sensible to be stored in that situation. If most numbers do
start with 0.
The easiest way is to write them in a table
Student number
Integer
1 byte
Student name
Character
20 bytes
Amount paid
Integer
1 byte
Emergency number Character
12 bytes
Form (e. The teacher decides to store the information as a
file on a computer. but 5 bytes would not. Emergency telephone number.
e.
Form (so that contact can be made in school).

Just make sure that you write down somewhere that you know that there are
1024 bytes in a Kbyte. this is only an
approximation anyway.
Note: Don’t worry about dividing by 1024.99Kbytes. in this case 37 bytes.
Therefore the size of the file is 1. so the size of this file is 2.3 Sizing a File
We have just designed the record format for a given situation.
All files need a few extra pieces of information that the user may not see such as
information at the start of the file saying when it was last updated.
There are 1024 bytes in 1 Kbyte. because.850 bytes) =2.035/1024 =
1. which file it is.
There are 50 students going on the trip. It may be necessary to
calculate how large the file is going to be. otherwise you can’t be given the mark for knowing that.
and it is usual to add 10% to the size of a file because of the need for overheads.850 bytes.035 bytes.850 bytes + (10% of 1.
The final stage is to ensure that the units are sensible for the size of the file. after all.3. is it
protected in any way? These sort of extra pieces of information are known as overheads. so the size
of the data in the file will be 50 * 37 = 1. If you gave the final answer as 2 (approx) then that is just as
acceptable.1.
Having decided on the size of each field. each of them having their own record. it is a simple matter of adding up the individual
field sizes to get the size of a record.
.

To look up
a particular name will still take a long time even though it is being held in sequence. but the data is effectively unstructured. It contains large volumes of data which can be used.1. However it is done the data has been arranged so that it is easier
to find a particular record. Imagine how difficult it would be to find a number if they had just
been placed in the book at random.
Sequential access. but that it has a structure that makes it accessible. So to
look up Jawad. the data is then searched alphabetically in sequence.3 Access Methods to Data
Computers can store large volumes of data. and that is how they should be read. It could have been stored in the order that they came in a Computing exam.l. having done this.
In previous sections of this chapter we used the example of a set of students whose data
was stored in a computer. The difficulty is to be able to get it back. The characters were all typed in. Reading this book would be impossible if all
the words were in alphabetic order. This method of access involves
looking up the first piece of information in an index which narrows the search to a
smaller area.
Serial access.
and consequently it should find the data faster.
There are a number of ways of arranging the data that will aid access under different
circumstances. If the data is in alphabetic order of name and the computer is
asked for Zaid’s record it won’t start looking at the beginning of the file. a J is found in the table which gives the page number 232. In
order to be able to retrieve data it must be stored in some sort of order.4.
This sort of data storage is only used when it is unlikely that the data will be needed
again. This is the simplest form of
storage. The data could have been stored in alphabetic order of their
name. to look up a
particular telephone number because they are stored in alphabetic order of the
subscriber’s name.3. so finding it again can be very difficult. fairly easily. Imagine the phone
book. like the names and numbers in a phone book. the search is
then started at page 232 (where all the Js will be stored). This
type of data storage is called Index Sequential. or by
age with the oldest first. in
order. The value of the book is not just that it contains all
the data that may be needed. or when the order of the data should be determined by when it is input. A good
example of a serial file is what you are reading now.
the structure of the data in a computer file is just as important as the data that it contains.
Perhaps it would be more sensible to have a table at the front of the file listing the first
letters of peoples’ names and giving a page reference to where those letters start. Another example of the use of a serial file will be
seen in section 1.
Imagine a large amount of data. Similarly.
.
Indexed sequential.
A file of data that is held in sequence like this is known as a sequential file.
Data is stored in the computer in the order in which it arrives. but at the end.

What would be wonderful is if.4.
. However. Jawad cannot be placed after Mahmood because
that is the wrong ‘order’.j. How this can be done is explained in section
1. the computer can work out where that data is stored.
A file that stores data in no order is very useful because it makes adding new data or
taking data away very simple. the user asks for Jawad’s record and the computer can go straight to it because the
word Jawad tells it where it is being stored. by looking at the
data that is to be retrieved. In any form of sequential file an individual item of data is
very dependent on other items of data. In other
words.Random access. it is necessary to have some form of order because
otherwise the file cannot be read easily.

216……. Yasmin. the account numbers for a bank’s customers are used as the key to access the
customer accounts. there is a new index for the next two
digits.3.g.
Khurram. and some questions will remain unanswered.
Dependent on the result of this first index search.. Saeed. no aids to searching. and no complicated methods for adding
new data..
Serial files have no order.
This leaves a space into which Hinna’s record can be inserted and the order of the records
in the file can be maintained. space must be found between Hameed and
Khurram. To do this all the other records have to be moved down one place.
…
Hameed. but would be split up by using indexing into what
amounts to a number of smaller sequential files.
Khwaja.
…
If a new pupil arrives whose name is Hinna. 21…………
Khurram. 169………. 317………
Khwaja. Ali. and then Khurram.3 Implementation of File Access Methods
This section is about how the different access methods to data in files can be put into
practice.
Because sequential files are held in order. 317………. held in order. Shaffi. either with
finding the data being searched for. because
it has to be placed in the correct position in the file.
Sequential access. that have those first
. The accounts are held sequentially and there are approximately 1
million accounts.
e.
Larger files might use this principle. which then points to all the account numbers. Yasmin. Shaffi. There will not be a lot of detail.
e. The data is simply placed on the end of the existing file and searches for data
require a search of the whole file. A section of a school pupil file might look like this
…
Hameed. or getting to the end of the file without finding the
data.
Naghman. starting with
Naghman. then Khwaja. There are 7 digits in an account number. Saeed.g.. all the records that come
after it have to be moved in order to make space for the new one.
Serial access. 216………. starting with the first record and ending.1. 21……. Ali.
Indexes could be set up which identify the first two digits in an account number.
Naghman. adding a new record is more complex. 169 ……. To do this.
Having to manipulate the file in this way is very time consuming and consequently this
type of file structure is only used on files that have a small number of records or files that
change very rarely.
don’t worry because those will appear in further work..

The data for Jaheed cannot be here because Jawad’s data is here. Therefore Jawad’s data is being held at address 40 in memory. There will be one index at the first level.
00
01
02
…
99
00
01
02
. The algorithm suggested here will
result in a lot of clashes which will slow access to the data. imagine that you are searching for Jawad’s data.
So Jawad = 10 * 04 = 40.. but each entry in there will have its
own index at the second level. this will give the address of the student’s data. so there will be 10.000
Final index blocks
each containing up to
1000 account numbers
Random access.
E. so
adding a new record in the right place is now manageable which it would not have been if
the 1million records were all stored together.
This is done by carrying out some arithmetic (known as pseudo arithmetic because it
doesn’t make much sense) on the data that is being searched for. But each block of records will only have a maximum of 1000 records in it.
This is called a CLASH.
The rules that we shall use are that the alphabetic position of the first and last letters in
the name should be multiplied together. 42..
To access a random file. and does not give good results.
Jaheed = 10 * 04 = 40. the simple solution is to work down
sequentially until there is a free space.
…
99
One
First level index
(first two digits
in account number)
00
01
02
…
99
100
Second level indexes
(third and fourth digits
in account number)
0102000
0102001
0102002
0102003
………. and so on until a blank space.four digits. A simple change in the
. so there will be 100 indexes at the second level. and if
that was being used.
The problem with this example can be seen if we try to find Jaheed’s data. as we shall soon
see. but it illustrates the principle. Any algorithm can be used as long as it remains the
same for all the data. When a clash occurs.
0102999
DATA
10.
This algorithm is particularly simplistic.000 blocks of data
records.
This type of algorithm is known as a HASHING algorithm.g. Each of
these indexes will have 100 options to point to. So the computer would inspect address 41. the data itself is used to give the address of where it is stored.

05. Having so much redundancy in the algorithm is obviously not
acceptable. If the algorithm is to write down the alphabetic
position of all the letters in the name as 2 digit numbers and then join them together there
could be no clashes unless two people had the same name. The trick in producing a sensible hashing algorithm is to come up with a
compromise that minimizes redundancy without producing too many clashes. 05. This is known
as REDUNDANCY.g. 13 giving an address 100108050513
The problem of clashes has been solved. 04 giving an address 1001230104
Jaheem = 10. Jawad = 10.
e.algorithm will eliminate all clashes. 01. 08. but at the expense of using up vast amounts of
memory (in fact more memory than the computer will have at its disposal). 01. 23.
. 01.

1. In addition
to the types of data that we have already described. because the next one to be printed should be the one that has been
waiting longest.
When the computer is expected to store data. it has to be told what type of data it is going
to be because different types of data are stored in different areas of memory. whereas the
British put the day first and then the month. for example.4. as the name suggests.3.g. data
types. The other is date. which is just a set
of characters one after the other). Care should be
taken with the date because different cultures write the three elements of a date in
different orders. but there are two others that are useful.
Answer: A queue. Questions based on this will be restricted to the particular
structures mentioned in 1. Americans put the month first and then the day.c and 1. E. State a suitable data structure for
storing the jobs that are waiting to be printed giving a reason for your answer.
.3 Selection of Data Types and Structures
Data types. It automatically places two digits
after the point and the currency symbol in.
Data structures
Students should be able to justify the use of a particular type of structure for storing data
in given circumstances. this stores the date in either
6 or 8 bytes dependent on whether it is to use 2 or 4 digits for the year. set up to deal with money. Jobs are sent to
a printer from a number of sources on a network.d and will be non-contentious.4. Currency data
is. more specialised. Most can be covered by calling them characters (or string data. there are other.

This is known as producing an ARCHIVE of the
data.
Data sometimes is no longer being used. for instance a past pupil may ask for a reference. If all the data has been erased
it may make it impossible to write a sensible reference. so a transaction log tends to use serial storage of the
data and is the best example of a serial file if an examination question asks for one.
The second problem is that the back-up copy will rarely be the same as the original file
because the original file keeps changing. In most applications the data is so
valuable that it makes sense to produce more than one back-up copy of a file. and
often.3. a
separate file of all the changes that have been made since the last back up is kept. A good example would be in a school when
pupils leave.
Archiving data. so that space
on the hard drive can be freed up.
It makes sense to take precautions against a major disaster. if the file now crashes.
but there are wrong ones. then the bank is out of business. If a bank loses the file of customer accounts because the hard disk
crashes. This copy is known as a BACK-UP. If a back up is made at 9. so that if the disk is destroyed. There are no right answers. the back up will not include the
change that has been made. It all depends on the application.
The first problem with backing up files is how often to do it. is irreplaceable.00am and an alteration
is made to the file at 9.
whereas a bank customer file may be backed up hourly. Speed of access to the data on the transaction log is not
important because it is rarely used. it is
used for storing little used or redundant data in case it is ever needed again. It has taken a long time to input to the system.05am.
Data stored in files is very valuable. All their data is still on the computer file of pupils taking up valuable space.
. but not quite. Once a new back up is made the old
transaction log can be destroyed. some of
these copies will be stored away from the computer system in case of something like a
fire which would destroy everything in the building. (Schools normally archive data for 7 years before destroying it). An application that involves
the file being altered on a regular basis will need to be backed up more often than one
that is very rarely changed (what is the point of making another copy if it hasn’t changed
since the previous copy was made?).
It is not sensible to just delete it. Because of this. This transaction log is very rarely used.1. The simplest solution is to
make a copy of the data in the file.3 Backing up and Archiving Data
Backing up data. Data that is no longer needed on
the file but may be needed in the future should be copied onto long term storage medium
and stored away in case it is needed. there are all sorts of reasons why the data may still be
important. It is very nearly the same.
Note: Archived data is NOT used for retrieving the file if something goes wrong. A school pupil file may be backed up once a week. This
file is called the transaction log and it can be used to update the copy if the original is
destroyed. the data can be
recovered.

Notice: (i) and (ii) It was necessary to show a method of working out. in part (i) this is obviously 8 bits and is an easy mark. so one of the
two marks is going to be given for showing the relationship between binary and
each of these two representations. a) (i)
128
64
32
16
8
4
2
1
0
1
1
1
0
0
0
1 =01110001. so it is necessary to show that you know what you are doing.Example Questions
1.
(4)
A.
Explain how the denary number –27 can be represented in binary in
(i) sign and magnitude
(ii) two’s complement
notation. Notice that for the octal answer it was necessary
to add a 0 to the front of the binary number to give 9 bits (3 lots of 3). so just writing the answer down is not
acceptable.
(4)
b) Using the answer obtained in part (a) show how 113 (denary) can be expressed in
(i) octal
(ii) hexadecimal.
(4)
A.
(ii)
1 = 0001
1 = 0001
3 = 0011
Therefore 113 = 0000000100010011
b) (i) 113 = 001 110 001 in binary
= 1 6 1 in octal. the question stated that the appropriate
number of bytes be used. Also. particularly the
value of the MSB in each case. using a single byte for each answer. but
in part (ii) it is necessary to add a set of zeros to the front of the answer to make it a
whole number of bytes.
2. a) Express the number 113 (denary) in
(i) binary
(ii) in BCD
using an appropriate number of bytes in each case. Many
students have calculators that will automatically change from one number system to
another. There will be a mark for showing the column headings. even if you
use a calculator to check the results.
(ii) 113 = 0111 0001 in binary
= 7
1 in hexadecimal. (i)
+/64
32
16
8
4
2
1
1
0
0
1
1
0
1
1 = 10011011
(ii) –27 = -128 + 101
= -128 + (+64 +32 +4 +1)
-128 64
32
16
8
4
2
1
1
1
1
0
0
1
0
1 = 11100101
Notice that the question asked “Explain…”.
.
(iii) and (iv) The question stated that the first answer had to be used.

3. (2)
b) State what is meant by Boolean data. In a question like this
try to ask yourself what evidence the examiner is expecting for the mark.
b)-Boolean data is data that can exist in two states.
Note: these marks go in pairs. Don’t worry if you are not happy with the last point. The other
marks are for using 8 bits for each value.
Describe how characters are stored in a computer.
this is a more advanced feature of arrays – look at the notes on section 1.c. a)-Integers are whole numbers
-Floating point numbers allow for the storage of fractions.
showing you working.
Add together the binary equivalents of 34 and 83. -Each character is given a code…
-as a binary number
-Each character code occupies one byte of data
-Typically one byte is eight bits
-Most computers use a standard set of characters like the ASCII set.
State three parameters that need to be given about the array before it can be used. and for the answer. using single byte arithmetic.
5.
-The number of dimensions of the array…
-so that the computer knows what form the data is going to be stored in.
There are lots of marks available here. -The size of the array (how many data items it will hold)…
-so that this amount of space can be reserved in memory.
-The type of data to be stored in the array…
-so that it can be set up in the correct area of memory.
4. The part that shows that you are
capable of doing the arithmetic is the carry. In part (b).
(6)
A. but they
are not really part of this syllabus.
explaining the reason why each is necessary.
6. don’t miss it out.
34 = 0 0 1 0 0 0 1 0
83 = 0 1 0 1 0 0 1 1 +
0 1 1 1 0 1 0 1 = 117
1
Note that the question asked for the working.g. e. The question has been left deliberately open
so that there are plenty of mark points available.a) Explain the difference between integer and floating point data types.
-The name of the array…
-so that it can be identified when it needs to be used. true or false. it will be given
the marks.
.
An array is to be used to store information. this is another standard definition. don’t try to elaborate too
much or you may wander too far from the answer.
(3)
A.4. If your answer is valid though.
(1)
A.
Note that in part (a) there may be lots of other differences that you know.
(3)
A.

A stack is being held in an array.
-Read values from old list in turn
-If plant in old linked list likes shade then…
-add to new list and put in pointer.7.
(2)
A. The second part is more difficult because it
means a certain degree of analysis of the problem to be able to solve it. a)
Head of list table
(Start Pointer)
Dahlia
Clematis
Sweet pea XX
Pansy
Mark points:
-Some start position for list
-List in alphabetic order
-Use of pointers
-Use of null pointer to finish list.
(ii) The stack pointer will be pointing at the first location in the array.
(ii) The array may be empty.
A garden centre stores details of each of the types of plant that it has for sale on a
computer system. The details of the plants are stored in alphabetical order in a
linked list. of plants that like shaded conditions. there is no value to be read. if you
draw a diagram and remember to start and finish it.
b)(i) The stack pointer will be pointing outside the array. Clematis. When discussing stacks and queues it is important to have a picture in your
mind of what it looks like. Stick to the simple type of diagram and don’t
forget how to start and end the list.
b)-Create new linked list by creating a new start point.
.
(4)
b)Describe how a new linked list.
8. but the array is perfectly adequate for this course.
(4)
A. can be
created from the original one.
a) State a problem that may arise when
(i) adding a new value to the stack
(ii) reading a value from the stack. Dahlia. The simplest picture is to imagine them being held in an
array. Sweet pea. Items may be read from the stack or added to the
stack. consequently no new value can be entered. you won’t go far wrong. This is why
there are rather more mark points available. This is not the only way to store them and you may have been shown other
methods. You may use
the following plants to illustrate your answer
Pansy.
a)By drawing a diagram show how the plants are arranged in the list.
(2)
b) Explain how the stack pointer can be used by the computer to recognise when
such problems may occur. a)(i) The array may be full.
-Repeat until null pointer (end of list)
-Place null pointer after last entry in new list
Note: The first part is fairly simple. When dealing with linked lists.
Notes.

000 books.6 Mbytes”. school numbers).000 + 148. Don’t worry about
trying to get the ‘correct’ answer. there isn’t one.
d)Total size of one record = 74 bytes
-Size of file = 74 * 20000 = 1480000 bytes
-+ Overheads of 10% = 1.480. state 3 other fields that it would be sensible for the
library to store in this file. any sensible fields (can you justify it?) are acceptable.
(2)
c) State the size of each of the fields in your record.
. this gives approximately 1. When you answer this question your
. although an
explanation would be accepted if it was clear what was meant.
A library stores details of the books that are available. ISBN. would be a sensible field. it is 10 characters long. giving a reason why each of your chosen fields would be
necessary. just make it sensible. In part (d) make sure that you convert your answer to sensible
units. There is a
correct answer for the ISBN. On the other hand 1000 bytes would
be way over the top and 10 bytes would be unreasonably small. but it is not part of your
syllabus to learn things like that off by heart. Publisher/so that more copies may be ordered.
E. so as long as you don’t say something
silly like 30 bytes.
c)
Title
40 bytes
Author
20 bytes
ISBN
10 bytes
Shelf
3 bytes
Category
1 byte
Mark points:
-Use of bytes
-Sensible field sizes. estimate the size the book file. For
instance.g. ISBN/to identify book
Shelf number/ to allow for ease of search for book
Fiction or reference or childrens’ (some form of category)/ to decide whereabouts in
library it should go
b)-Book number (ISBN)
-because it is unique to that record and hence can be used as an identifier.
Notes: In part (a). Don’t worry about using a calculator.
(2)
d) If the library stores approximately 20.55 Mbytes.000 = 1.628.(Divide by 1024 until sensible units) = 1. Try to be aware of
the standard key fields (account numbers. you
will get the mark.
(3)
A. a)One mark for each of three sensible fields with an extra mark for an explanation
of the need for that field. which demonstrates that you don’t know what an ISBN is. If you suggested 100 bytes for the
title it would be accepted as being reasonable. In this case it would be quite acceptable to write “Keep dividing by
1024.
(6)
b) State which field would be used as the key field of the record and explain why a
key field is necessary.
a) Apart from title and author. as long as you show that you did know
the correct method is to divide by 1024. The
sizes of the fields are only given as guidance.9. barcodes. an approximate answer is all that is
necessary.000 bytes.
In part (b) you would be expected to provide the answer ISBN.

(2)
b)Describe what is meant by a hashing algorithm and explain why such an
algorithm can lead to clashes. or if a book is replaced by a more upto-date edition.
a) Describe how the library can implement a sensible system of backing up their
files. don’t worry.
-Sequential file holds the data according to some order defined on the data. the examiner will
mark your answer and not expect it to be the same as a model answer.
-Back up copies would be stored away from the building with the computer system
in it to ensure that a copy of files survived in case of fire.
-When members leave the library the data should be archived…
-also when they have not taken a book out for a long period of time their record can
be considered to be dormant.
(4)
A.
b)-A hashing algorithm is pseudo arithmetic…
-carried out on the data…
-in order to determine the location of the data in the memory.
b)-When books are discovered to be missing.
-Multiple copies of the book file would be made
-Member file copies and transaction logs may be kept for a number of back up
periods. Note that there are
plenty of mark points available in this question.
-A clash occurs when the answer to the pseudo arithmetic is the same despite the
data used in the calculation being different.
.
(4)
b) Explain the part that would be played by archiving in the management of the
files.
Notes: Backing up and archiving are topics which cause confusion among
candidates. this is not required
and will earn no marks. The library does a stock take
twice a year and orders new books only once a year.
11. There really is no need for such confusion if you remember that
archiving has nothing to do with recovery after a disk failure.answer is highly unlikely to be the same as this.
a)Explain the difference between a serial file and a sequential file.
A library keeps both a book file and a member file. the old records should be kept…
-but they are no longer live so are taken from the hard disk…
-after a copy (archive) has been made. Restrict
yourself to what the question is asking.
(3)
A.
Note: This is a question where it is very easy to try to answer too much.
10.
-Member file needs backing up daily(at least weekly) because of constant
changes…
-would also need to keep a transaction log for the member file. a)-Book file needs to backed up twice (or three) times a year…
-when the stock take or book purchasing has made the file alter. a)-Serial file holds data in the order in which it was received. Members can join or cancel
their membership at any time. Many candidates faced with part (b) will go
into great detail about what to do after clashes have occurred.

The parts of the operating system.
The control unit has three jobs
1. The ALU contains circuitry that allows it to add numbers together (do arithmetic). any complicated diagrams showing how the various parts of
the processor are connected up and communicate with each other do not appear in the
syllabus until next year. This is the job of the control unit. and carrying them out.
3.
1. and Arithmetic Logic Unit
The first thing to be said in this section. It has to tell other parts of the processor what they should do so that the instruction will
be carried out. Memory Unit. Likewise. These instructions are
in a particular order in the program. Something.
1.
2.4.
. has to manage the instructions and make sure that all the other parts of
the processor do what they should be doing. It allows for logic decisions to be made (If the value is negative then …. in other words it has to work out what needs to be
done to carry the instruction out.execute cycle. One of the jobs of the control unit is to be able to find the information
stored there when it is to be used. the part of the
processor that makes the decision is the ALU). will
mean that the computer has accomplished whatever task it was meant to do.1. and following them. The three topics that are
listed in the heading would normally lead to the fetch. It has to decide which instruction to carry out next and then go and get it. is what is not necessary.
3.
Arithmetic Logic Unit (ALU)
The ALU is where things are actually done in the processor. which the computer is using at the time. All input and output to and from the processor goes into the
ALU and waits there while the control unit decides what to do with it.
in the computer. The requirements of this section are very simple.
All computers follow instructions that are given to it in a program.
Memory Unit
The third part of the processor is where everything that the processor is going to use is
stored.
Control Unit. It has to decipher the instruction. also need to
be stored in memory. This includes all the program instructions and all the data needed to carry out
those instructions.4 Hardware. this does not come
into this module. they are
restricted to a basic understanding of what these three parts of the processor are meant to
do. The third task of the ALU is to act as the gateway between the processor and the other
parts of the computer system.1 Control Unit.
2.

These will be discussed in section 1. This little program is called
the bootstrap. so a small program is stored on ROM whose job it is to go and get the operating
system from the hard drive so that the computer can work. The BIOS itself includes user defined parameters and hence is not stored in
ROM entirely. but that means that if you want to use your computer in a different way or you
want to install the latest edition of an operating system to replace the one in use. there
are plenty of other places that a computer can store data or programs e. as those who have used a computer will know. A typical question will ask for an example of what is stored in ROM and RAM. SRAM.5. Anything that is being held elsewhere. whereas ROM is non-volatile because it cannot change.5. The primary memory of the
computer is the memory that is advertised as being “128 Mbytes of RAM”. This simply
describes the capacity of the memory. A problem arises because
when the computer is switched on it needs the operating system to be able to do anything
useful. and the process of retrieving the operating system is known as booting.
EPROM. don’t worry. in fact it is probably better not to until the
later parts of the course.2 Types of Primary Memory
The first question that needs to be answered is “What is Primary Memory?”
In section 1. However.
There are a number of different types of memory in the processor. but in most micro systems it isn’t for the reasons given above. There are many other types of primary memory that you may have heard of (PROM. RAM is said to be volatile memory because it is so easily
changed.1.
2. In fact the BIOS tends to be stored in a special type of RAM which is
refreshed using battery power when the system is switched off.
.…). When the computer is
switched off all this data is lost.c.
2. This is past the level of
this course and students are advised not to use this as an example of storage in ROM. DRAM.
The BIOS (if you don’t know what that is. In the past the whole operating system was stored on
ROM. you
can’t because the computer can’t delete the old one. They are all a type of either RAM or ROM and
you have no need to learn about any of them. This means that even switching the computer off
will not effect the contents of the ROM. There is very little that needs to be stored in
ROM so it tends to be very small. When the computer is turned on it
would be there. The
safest answers are the bootstrap being stored in ROM and user software and data being
stored in RAM. In the previous section it was stated
that any data or program instructions that the processor was to follow had to be in the
processor memory.
Notes:
1.4. For this reason the operating system is stored on the hard drive of a
computer along with all the other programs that may be used.g.
Because it is so important it is called the primary memory. RAM (Random Access Memory)
RAM stores the programs that are being used by the computer (including the operating
system) and the data that is being used with those programs. like on the surface of a disk
drive.
1. it is not in the course) is another
problem. ROM (Read Only Memory)
ROM is memory that cannot be altered. a disk drive or a
CDROM. Problems arise if a student answers that the operating system is stored in
ROM because it can be. EAROM. cannot be used by the processor until it is moved into the processor’s memory.a the concept of the processor needing to store data of all types in the
memory was introduced.

2. it is more likely that they will be fixed
to the chassis of the machine because of the tolerances that they have to work to. Although they can be portable. However. A CDROM is an optical storage device.
3. In addition. allowing for easy communication of data from one stand-alone computer to
another. Large quantities of data can be stored on the surface
and it is completely portable from one machine to another. and it is contained in a sealed
unit.Magnetic hard disk
Data is stored in the same way as on a floppy disk. or locked away in a
safe.Secondary Storage Media
Primary memory is memory within the processor. almost all microcomputers having a floppy disk drive. can it be moved around easily
 Access times to the data stored. However. as are commercial files of data.
There are a number of different types of secondary storage that can be categorised
according to
 Means by which the data is stored. Despite being direct. large volumes
of data can be held and the medium is freely transportable. Most software is too large to
be stored on a floppy disk. It is also readily available. access times are slow because of the limited speed of rotation
possible and the relatively crude nature of the read heads. consequently that the
amount that can be stored is greater and that the access times are much faster. a floppy disk is very
portable. These differences mean that the hard disk can rotate faster. sequential storage or direct access storage
 The capacity of the medium. It is here that the computer stores data
that are in current use because the control unit does not have direct access to data that is
stored anywhere outside the processor. The differences being that the hard
disk is made of a rigid material rather than a floppy plastic.
1.Magnetic floppy disk
Floppy disks hold a relatively small amount of information. using the reflection of a laser off a
pitted surface to store information. the storage that is available in the
processor is limited in size and volatile. how much can be stored on it
 Portability of the medium. having very large
storage capacities. However. Magnetic tape
Magnetic tape is still widely used. particularly in the form of tape streamers. the heads can get closer
to the surface meaning that the storage density can be greater.CDROM
A CDROM is different from the storage devices so far mentioned because it is not
magnetic. It is called secondary storage. The hard
drive is likely to be the main secondary storage for a computer system. most computer
. What is needed is something that is less
temporary in nature and that does not have the same restrictions as far as size is
concerned. by necessity. sequential which
makes it largely unsuitable for most data handling applications.
It is also convenient for storing those files that are particularly confidential because the
files cannot be broken into if they are being carried by the owner.
4. optically or magnetically
 The technique used for storage of the data. These qualities make it
valuable for producing back up copies of files stored on a computer system. The big
disadvantage of tape is that the access to the data stored is. This will be memory outside the processor.

Capacity.
A floppy disk has the advantage that it can be written onto and taken away from the
computer. and a CD is not alterable by the user.
A Tape Streamer is used for making backups of files held on computer systems.
Notice that there are no figures quoted for access times.Others
There are many other types of secondary storage. DVD is a relatively new technology that will probably replace CDROM
as it can store much larger quantities of data and allow access at high speed. having a faster access speed and a
greater capacity. If the author were to quote a number. some other method of sharing will have to be
devised if this is not true. it is impossible to say that one is faster than the other. There is little point in doing this
because access times vary according to the manufacturer and the point of development so
far reached.
5. much depends on the type of drive or size of medium being used. Add to this the fact
that all computers can be relied on to have a floppy disk drive and it becomes a sensible
way of transferring information from one machine to another.
Uses. but tend to be comparable in capacity with smaller hard drives.
For these reasons. Access times from CDROM and hard drives
are faster than the other two. but the above points are still true. Because of this it can be used for storing confidential files. but the disadvantage of the
access being slow does not matter because it is rare that a backup file would be used
anyway.
A CDROM cannot be altered (unless it is a special re-writable). a reasonable analogy is that a floppy would store the text
from a book. two of which are worth a mention.systems can now be relied on to have a CD drive. These advantages mean that it is going to be used for storing software and user
files. Zip
drives are a more robust version of a floppy disk. manufacturers have tended to use CDs to produce software and large
data files like encyclopaedias. In general terms the tape streamer is the slowest access
because of the way that the data is stored sequentially. Tape streamers
come in different sizes. However. while a hard drive
could store a library. For the
purposes of the syllabus. there are some obvious uses for
each storage type which take into account the advantages and disadvantages of each.
Of the different types of disk. This disadvantage can be
turned into an advantage if the owner does not want the contents of the storage to be
. then comes the floppy disk which
suffers because of the nature of the medium. but it would certainly be out of
date by the time you read it. a CDROM would store a multi volume encyclopaedia.
Obviously. not only would it be wrong as far as
this work is concerned because there is such a wide range. They have become fairly popular for backing up work on
microcomputers. no list of uses will be complete.
Again. It is now possible to write to CDs by using a special
peripheral device called a CD writer and a special CD. the original 4 types of secondary storage are quite enough at this
level. The disadvantage of being attached to one machine is not important if the same
users always use the same machines. but because there is such a range of both types of drive
available.
Speed of access to data. This
makes use of the fact that it can store a large amount of data.
A hard drive has the advantages of being fast to access and also stores massive amounts
of data.

6. including Buffers and Interrupts
There are two places where data can be stored in a computer system. Sometimes it is necessary to transfer data from the primary
memory to secondary storage. needs to move the data
into the primary memory first. consequently.
. so the diagram should look like this
Primary
Memory
ALU
Secondary
Storage
This causes a problem. Sometimes it is necessary to
transfer from secondary storage to primary memory. while the secondary storage is probably some sort of disk or tape which
(while it seems incredibly quick to us) is very slow at reading or writing the data. This problem is overcome by the use
of a buffer. Whichever direction the data is to be transferred the
method of transfer must be planned.d.
Normally the data would be transferred through a wire connecting the two storage areas
together.3 Transfer of Data. Unfortunately. it can’t because it needs the
ALU that is being used for the transfer of the data. the primary memory
and secondary storage. This means that the processor should be able to get on with something else
because the secondary storage is so slow.
1.altered. perhaps because the computer is going to be switched off
in which case the data in primary memory would be lost. The primary memory operates at great speed because it is part of
the processor. The type of wire and the different rules for data transfer are explained in section
1. sufficient for the moment is to have a picture of data travelling freely in both
directions. in
comparison. we know that things can’t be that simple.4. We know that primary memory
is part of the processor. and that anything that goes in or out of the processor must go
through the ALU. Examples of files stored on CDROM are software for import to a system and
large reference files like encyclopaedias. perhaps because the processor wants
to use some data held in the secondary storage and.
Primary
Memory
Secondary
Storage
Unfortunately.

a printer or a keyboard. but further complications can
wait until the second year of the course.Buffers. the solution is to put a small amount of fast memory in to the system between
the ALU and the secondary storage device.
An interrupt is the message which the secondary device can send to the processor which
tells the processor that all the data in the buffer has been used up and that it wants some
more.
Notes:
A buffer is a small amount of fast memory outside the processor that allows the processor
to get on with other work instead of being held up by the secondary device.
The problem is caused because the secondary storage device is so slow compared to the
processor.g. This small amount of memory between the two parts of the system is called a buffer.
This system is fine if the buffer can hold all the data that needs to be sent to the storage
device. the whole procedure is repeated. When the
processor receives the interrupt.
. but
the same is true for any communication between the processor and a peripheral device. This forces the processor to stop what it is
doing and fill the buffer up with more data. the storage device has to
be able to tell the processor (actually the control unit) that it has used up all the data in
the buffer and that it is ready for the next lot. However.
The example used here was communication between primary and secondary storage.
The system is not really quite as simple as suggested here. if there is more data than will fit in the buffer.
e.
Stage One: Filling the buffer from the processor
Primary
Memory
ALU
Primary
Memory
ALU
Buffer
Secondary
Storage
Buffer
Secondary
Storage
Stage Two: Emptying the buffer to storage
Interrupts. and then get on
with something else while the storage device takes its time in reading (or sending) the
data.
This means that the processor can send data very quickly (or receive it). Because this message from the secondary
device makes the processor stop what it is doing it is called an interrupt.

by inclusion in the syllabus there are some that must be understood.c.g. which are sensitive
.
a) Keyboard. The first problem is very difficult
to solve because of all the experienced operators that can use the present keyboard so
well. keyboard. The design is not very good for two reasons.
However. e. making it
awkward to keep your arms comfortable while using it.
3.
1. for instance most calculator keyboards are very different.6. A different type of keyboard. where
the keys are simply part of a continuous surface which has areas on it. Keyboards are the
most common form of input device to a system because they are universally available and
understood. Most keyboards contain the letters of the
alphabet. Retraining them to use a different arrangement of keys would not be feasible. Communication devices. but not all do. have been
described in section 1. First. the
arrangement of characters comes from the original typewriter whose keyboard was
arranged to be the most difficult to use in order to slow typists down so that they did not
jam the mechanism of the old machines. specific questions will not be asked about other input devices with
the following exceptions. candidates should be encouraged to learn about a variety
of contemporary devices so that they can use them when answering questions that ask for
a hardware configuration for a specific application.
2.
There are too many different input devices to expect familiarity with all of them.
These devices allow for communication between machines and will be covered in detail
in section 1. Storage devices. is called a peripheral device. While this
list is not exhaustive. Input devices. The characters needed for specialist use
machines are determined by the use to which the machine is to be put.
mouse.Common Peripheral Devices
Any hardware device that is part of the computer system but is not part of the processor
itself.b.
Peripheral devices can be categorised under four headings. These are called natural
or ergonomic keyboards.
These devices. Additionally. as are
the keyboards for use at ATM machines.
One problem with normal keyboards is that they are particularly prone to damage from
dirt or liquids because of the gaps between the keys.
Various attempts have been made to address the second problem by arranging the keys in
curves that fit the palm of the hand rather than in straight lines. There are some devices that are so common that any candidate
taking an exam in computing can be expected to have experience of using them. A standard keyboard uses keys that stand for the different characters that the
computer recognises in its character set. which provide for secondary storage in a computer system. The second is that the keyboard itself is difficult
to use comfortably because of the way that the keys are arranged in rigid rows.5.
The common keyboard is known as the QWERTY keyboard because those are the first
six characters on the top line.

OCR tends to be an unreliable form of input and works more
effectively when it is restricted to having to recognise a standard character set produced
by printing rather than by using hand writing. if the barcode is damaged so that the laser scanner cannot read it properly.
A type of keyboard not yet mentioned is a musical keyboard. The value is that the characters are readable by humans and by
machines. The characters are printed
using magnetic ink. The different widths
of pairs of lines make up a code that can be converted into a number.
known as a MIDI (musical instrument digital interface) this connects the musical
keyboard to the processor and allows data to be passed between the instrument and the
processor.
c) Barcode readers. The
details of the contents of the barcodes are not of importance to us in this section. except
to say that barcodes can easily be misread by the system. This is a device that reads characters and can
distinguish between the different characters in a given character set. Called touch-sensitive keyboards. A barcode reader is a laser scanner that reads the reflected laser light
from a series of dark and light coloured lines of varying thickness. or concept
keyboards. A mouse is a device designed to be used with a pointer on the screen. which is done by using a switch (the mouse buttons). An example is the tracker ball used in many laptop computers. This is a device that reads characters that are
printed on an original document at the time of it being created. It is
particularly useful because it mimics the natural human reaction of being able to point at
something. The only common use for such characters is the data printed on the bottom of
cheques containing account identification.
although. and the other is the
ability to select.to pressure. This is necessary because when using a laptop there may not
be a flat surface available. Barcodes
are particularly useful because they do not rely on human beings to input the data. can overcome this problem. Barcodes are used where the data does not change. One is the movement around the
screen created by actually moving the mouse in a physical way. This digit is
called the check digit. OCR is used for reading post codes on
. the
digits represented by the code are printed underneath so that they can be input by a user
at a keyboard.
e) OCR (optical character reader). It works by
comparing the shape of a scanned character with a library of shapes that it is intended that
it should recognise. A mouse is really two input devices in one. This is like
an upside down mouse where the user moves the ball directly rather than moving an
object around a flat surface. and will be discussed in more detail later in the course. Variations have
been developed which use the same basic principles but are designed for particular
applications.
b) Mouse. they are ideal for use outside because rain will not damage them like a normal
keyboard. This number can
then be used as the keyfield relating to a file of items that have been barcoded. and so can be printed
on original packaging. Normally arranged like a
piano keyboard these need a special piece of hardware to allow them to work properly.
d) MICR (magnetic ink character reader). so one of the digits in the
number is used to check that the rest of the code has been read properly.

If you
consider the contents. the
same thing is true about output as is true about input.
The big advantage of both OCR and OMR is that data can be input to a computer system
without having to be transcribed first. A scanner is a device that converts a document into a series of pixels (picture
elements – these are small squares that. that it is important to know about
those devices stated in the syllabus and also a range of devices that will allow for sensible
decisions about peripheral devices to be made for a given scenario in a question. thereby cutting down the number of errors on data
input. that is
why OMR documents tend to be printed in a light blue or pink colour. one for present and one for absent. the better the picture will be. The difference is
the position that the mark occupies on the paper.
4. A typical use for a scanner would be to input a picture of a house so that
it could be included with the details of a house that is for sale in an estate agent’s
publication. the better the definition
of the final picture.
The user can then draw on the paper and the tablet will sense where the pencil is pointing
and transfer the line to the screen. there is no reason for any further sophistication to be necessary. not to be confused with a plotter which is an output device. this is known as the screen
resolution. a computer system running a modern game program will need colour and many
more pixels in order to produce a satisfactory picture. Again.printed documents and also for reading documents for blind people. The larger the
number of pixels. monochrome screen. but all use the same principle to
create the image. This is being typed using a very low resolution.
. Printing in the sensitive areas of the
sheet is done using a special type of ink which the optical scanner does not see. also according to the number of pixels that there are on the screen. A graphics tablet is a flat surface on which a piece of paper is placed.
a) Screens. The other standard
use for OMR documents is as multi choice examination answer sheets.
A scanner is an input device. The position of the mark conveys information to the machine.
i) Microphones. Monitor screens are categorised according to the obvious
colour/monochrome. There are different types of scanner. the contents of which
can be output using a voice synthesizer.
f) OMR (optical mark reader). or conversely the smaller each individual pixel. Output Devices
There are too many output devices to be able to write notes on all of them. The same action
(shading in a rectangle) stands for both being present and being absent. when put together. the higher the resolution is said to be.
However. Used to input sound to a computer system. This device can recognise the presence of a mark on a
sheet of paper.
h) Graphics Tablet. For
example a school register may consist of a list of names of pupils in a class together with
two columns of small rectangles. form a picture).
The more pixels there are.
g) Scanners. The more pixels that there are on
the screen.

b) Printers. The cost is more than
with the other types but used where it is necessary to give a good impression. Used to output sound from a computer system.
Laser printers can produce very high quality work at high speed. These tend to be slow. e. called a touchscreen. back to back.A particular type of screen. Information is output by the system onto the screen and the user is invited
to answer questions or make choices by pointing at a particular area of the screen. In other words the mark will not be for a
keyboard or a mouse. as has been mentioned. which produce output by spraying ink on to the paper could not produce
the two copies that the dot matrix can. but
the candidate will be expected to give sensible suggestions for each of the four areas of
peripherals mentioned at the start of this section. The image is created by pens being moved across a piece of
paper. but for suggesting sensible methods of input to the system.
Plotters are a type of printer designed for drawing lines and geometric designs rather than
for producing characters. and the output is particularly
poor quality. for instance
sending letters from a solicitor’s office to clients. under the command of the processor.
c) Speakers. their uses. This makes ink jet printers ideal for home use. Plotters tend to be used for drawing
blueprints. The
device can sense where the user is pointing and can report the position to the processor. Touchscreens are particularly useful in areas where keyboards are not
appropriate. This output is known as hard copy.
. A good example of this is the receipt that a shopper is presented with
if buying something using a credit card. however that is enough to be able to answer questions
in the exam. very young children who
want to be able to draw on a screen. at low cost. one
for the shop to keep and one for the buyer to take away with them.
Ink jet printers.
The processor can then deduce what the user’s reply was according to the position that
was pointed to. acts as both an input device and an
output device. The important thing to remember is
how the marks will be awarded. There will not be a mark for every device mentioned. but it can produce much better quality and in
colour. there are two copies produced.g.g.
There are many other peripheral devices and. e. There are many different types of printer and the student should be
aware of a number of them.
The first type is a dot matrix printer. However. there is
no need to understand how they work. Because of the physical nature of the way that the printout is
produced. They are also useful for
users who would find difficulty using other input devices. A printer is a device which provides the user with an output from the system
which is permanent. The questions will normally take the form of presenting a scenario and then
asking for a description of the hardware required. The big advantage is that the output is produced by using pins to strike at
the surface of the paper. so a printer is a device which
produces hard copy. a knowledge of
some others will not come amiss. it is possible to obtain multiple copies by using carbon paper or self
carbonating paper. where the device may suffer from vandalism. advantages and disadvantages. perhaps in an architect’s office to produce detailed drawings of buildings for
builders to follow.

Peripheral Hardware for a Given Application
This section deals with the needs of the application rather than the peripheral devices
themselves. any
physical disabilities which may make some hardware impossible to use. consideration
must be given to their age (can they read is an obvious question). compare the requirements of the
system with the characteristics of the available hardware devices. and the human being that is using the computer. consequently there are also speed mismatches on both communications
concerning peripherals.
When answering questions drawn from this section. then a method needs to
be found to keep the slowest parts of the systems isolated from the processor.
 Under what circumstances will the system be used? If the input and output devices
are to be used in the open air then the environment will dictate some restrictions
which would not be necessary if the system was being used in a computer room. their understanding of the software in use (do they need to be
given instruction how to use it or do they know what is expected of them?). but if there is a shortage of processing time.
.
When peripheral devices are chosen a number of factors need to be taken into account. consequently it will also have an
influence on the peripherals that are suitable for that input and output.
Speed Mismatch
A typical computer system will consist of the processor to do the necessary calculations
or other processing. output and storage of
data/information. This difference in
speed is known as the speed mismatch between the operator and the processor. the peripheral devices to allow input. If a computer is being used to control the insertion of the
graphite rods into a nuclear reactor it may become important to ignore the human being
once the decision has been made and simply to report that an action has been taken after
the event. their ability with
computer systems. but are considerably slower than
the processor. Peripheral
devices work at far greater speeds than the human being.
The speed mismatch causes more problems if the decisions of the computer need to be
acted upon immediately. If there are enough computer systems this speed mismatch does
not matter so much. One way of
doing this is to use batch processing (see module 1).
The processor can carry out its side of the task at great speed while the human being is
very slow both at providing input and making sense of the output. In this way the speed mismatch has been overcome by cutting out the slowest
part of the system. The software will dictate the type of input required
and the type of output that will be produced.
 Is the system automated in any way? If so the peripherals may include sensors and
actuators. and be prepared to state
why a particular choice has been made.
 Who are the people that are going to use the application? Specifically.
 The software that is being used.

Notice that the reasons given related to
the answers given in part (a).
Notice the way that the answers have been phrased in part (a). The question asked
for a comparison of ROM and RAM so both need to be mentioned when you are
giving an answer. “user files because there
.
giving reasons for your answers. 1. if the question had said ‘Describe…’ or
‘Explain…’ instead of ‘State…’.
b) -RAM would contain user files and software that is in current use. However.
Part (b) is asking for reasons to be given. implying that the original
software will need to be erased so that it can be replaced. but does not answer the
question until you say that ROM is not.…. whereas the data stored in ROM cannot be
altered. The part (b) answer is not. (The processor can use the
ALU to decide whether one value is greater than another. (This normally takes the form of
addition. The sensible response would
seem to be to number them.
and then make decisions based on the answers)
3. Any item of
data which is bound for the memory must be stored temporarily in the ALU while
the processor decides where it is going to be stored)
Notice that the question asked for three answers.
-RAM is used for these files because they have to be alterable. This program must not be altered because without it the
computer cannot start to work.
2.Example Questions.
(3)
A. a)
b)
A. Communication with peripheral devices is carried out via the ALU. and the result is stored in the ALU temporarily before being returned to
the memory)
2. or if one is negative. and some extra detail.
-ROM is used to store the bootstrap program. To say that RAM is volatile is true. Losing these files when
the machine is switched off is not a problem because they will have been saved on
secondary storage. Any arithmetic is carried out in the ALU.
-ROM is used because when the computer is initially switched on there must be a
program present that can be used to load up the rest of the operating system from
secondary storage.
State three functions of the arithmetic logic unit.
State two ways that RAM and ROM memory differ. while
ROM is not. The contents of the brackets give extra information which would not be
expected in this question. and the user will
want to use different software from time to time. would have
been necessary.
-The contents of RAM can be altered. (All data
which is to be used by the processor has to be stored in the memory.
(2)
Explain what types of data would be stored in each of RAM and ROM memory. for instance the contents of the brackets. The expected answers are the three single line
responses. Logical decisions can be made by the processor. then the question would have been worth 6
marks.
1.
(4)
a) -RAM is volatile (will lose its contents when the power is switched off).

if the two answers are mixed together then it produces a
confused. What happened to tape?
After all that is the first secondary storage that was mentioned in the text. Tape is
not sensible in this example. you
are getting used to this because it is generally true in most questions. wrong. there is not a big enough volume of data to make a
tapestreamer worthwhile.
-When the secondary device has used the contents of the buffer…
-it needs to tell the processor that it requires more data…
-this is done by sending a message to the processor.is more space in RAM”. but it makes clear what is being done.
4.
A student has a home computer system. so that important work is not lost if the hard disk crashes. word processor and essays)
-Floppy disk drive…
-to enable work to be transported between school and home so that it can be
continued in the evening
-CDROM…
-to allow the import of new games to the PC. so four devices seems sensible. but in
A. although that could be right if phrased a little more
carefully. Hopefully.
State what storage devices would be used on a home computer system and justify
the need for each one. and the old cassette tape is an antique by now. and often.
Notice that the question does not specify how many devices should be mentioned.
Also.
but it gave a good reason for wanting to do so in this case.
(8)
A. Notice.
Describe how buffers and interrupts can assist in the transfer of data between
primary memory and a secondary storage device.
-Buffer is an area of fast access storage. Transfer in the other direction is equally valid and gives rise to a
similar answer.
However.g. there are more mark points than there are marks available. also.
3. answer. the answer did not just say that it could be used to transport files.
-Zip drive…
-to back up the files.
. (4)
For the purposes of this answer I will assume that data is being transferred from
the processor to the secondary storage. However. You don’t have
to say this in your answer. In this
question there are obviously two points for interrupts and two for buffers.
Consequently. called an interrupt. a tape device does not fit the application given. for
a floppy drive. the
way that the justification for each of the devices was linked to the application. This is why the first statement is important as
it has set the parameters by which the question will be answered. -Hard disk…
-to store software and user files (e.
Notice that the answer describes transfer of data from the processor to the
peripheral..
-which can be filled by the processor and then emptied at slower speed by the
secondary storage device…
-allowing the processor to continue with other tasks. each device has to be named and justified (2 marks) and there are 8
marks for the question.

otherwise you haven’t
defined what an interrupt is.
(6)
Input:
-Touchscreen
-Some protection against vandalism/restricts user access to contents of menu
system displayed/simple to use because it uses human reaction of pointing so no
training necessary
Output:
-(Touchscreen)/printer
-Touchscreen outputs choices for user to select from/printer available for
producing hardcopy as a permanent record for the customer
Storage:
-Hard drive/CDROM
-Hard drive necessary to store details of the products on sale because of the large
number of changes that occur in this file. while the operator works very
slowly.
-The decision to change the speed of the line must be taken very quickly or product
will not go through all the manufacturing processes. The different departments remain in the same places. State a sensible hardware
design for such a computer system. In reality.
Notes: There is virtually no other question that can be asked about the speed
mismatch.
. so the computer controls it. but
this would mean that they would be able to communicate with one another. for the interrupt. It is simply the difference in reaction time and if the candidate can relate
that to the application.
(3)
A. the marks are split up according to the four
types of peripheral mentioned in section 1.
So.
-The computer is able to take decisions very quickly..
but such a question would normally have 8 marks. they must get the marks.
5.order to get the marks you must make sure that the definition appears somewhere. In this type of question you can’t expect a lot of marks for simply writing
down a long list of peripheral devices.
Notice the large number of possible mark points.e. you need to earn the last mark point. giving reasons for your choices of hardware. CDROM used to keep the store plan and
the location of the departments as these do not change. 2 marks for each of the types
of peripheral.5. Also the way that the marks are
split up. but the articles
available in each department change on a regular basis.
Explain why speed mismatch would mean that the computer should be in control of
the speed of the production line.
A. As
communication comes in the next section it was left out of this example question.
6. -Speed mismatch is the name given to the difference in reaction time of the operator
and the computer. this question would
probably have talked about such systems being available throughout the store.
A department store decides to place a computer system by the main entrance to
the store so that customers can find out whereabouts in the store items are
available.

1. Also those printers may be different types that could be used for
different tasks. to share
copies of software and to allow multiple access to files of data. This means that the systems
we have discussed so far are not connected to other machines. networks over small distances
are called Local Area Networks (LAN) while those over great distances are Wide Area
Networks (WAN). Generally. Every time the lesson ends you would need
to store your files on secondary storage. to share information centrally.1. It would be possible to store the files on a floppy
disk and take them away with you. but single processors.
A network of 20 computers in a school classroom is obviously on a small scale. This means that the type of printer used is dependent on the job that the
user wants it to do rather than the type of printer that happens to be connected to the
computer on which the work is being done. When computers are connected together to share files they
make a network. In a LAN there is the
added benefit of being able to share hardware. so the classroom with 20 computers may
only have 3 printers. not
because 20 is a small number.
Whether the network is a WAN or a LAN it will have the advantage of offering the users
the chance to communicate with one another.
Imagine a classroom with 20 computers in it. It would be much more sensible to have a system that allowed access to
the same files through any of the 20 computers. if longer the network is a WAN
 Networks allow computers to communicate
.
To summarise:
 Computers can be linked together to form networks
 If the distances are short the network is called a LAN. but because the communication is made easier because of
the short distances involved. This means that the next time you want to use those files you need to sit at the
same computer. but the likelihood is that the files will be stored on the
hard disk.5 Data Transmission and Networking. If a business with head offices in London and factories in
Karachi and Hong Kong wanted to connect the computers on the three sites up there is an
obvious problem of distances to be overcome.
sometimes with more than one user.5 Networks
All the systems that have been mentioned so far have been individual computers. To allow this the computers need to be
connected up to each other.

.
Networks allow the sharing of both hardware and software.

there may be a printer server to control use of the
printers. There is a need for something to control the signals being
transmitted.
 The computers need to be connected in some way. This is done by another piece of hardware called a modem.
. Actually
the cables already exist to do this. In order to send a computer signal down a telephone line it must be
altered first.
A wide area network differs because the distances involved tend to be far greater than for
a LAN. The cable has a limitation
in that the signal gradually deteriorates as it is sent down the cable which means that
the maximum length of the cable is about 300 metres. this is known
as network software or a network operating system. The cable is coaxial. It
is necessary to have a set of instructions that the network must follow. The standard method in schools is
to use a cable. Some networks have a number of different servers controlling different
parts of the system. they can simply ring each other up! Unfortunately.
In order to connect computers in a network there are a number of essential things
necessary
 Each computer needs to be able to communicate with others.
it is known as a server or a network server. In order to do this there
needs to be a special piece of hardware attached to the processor. the telephone system. communications are going to
get complicated. So to connect two computers
over a long distance. This maximum depends on a
number of things. It is through this network card that the computer can communicate. but all cable is ultimately
going to be limited in length. like a television aerial.
 The communications around such a system are obviously quite difficult to control. for example. A similar modem
must be present at the other end of the line in order to turn the signal back again. This job is carried out by a computer whose job is to control the network. because of this it is sometimes known as the
file server.
 With a number of computers attached to the network. Consequently it is not possible to connect all the computers by a cable. the type of
signals produced by a computer are different to the type of signal that can be sent down a
telephone line. On many LANs these server functions are all carried out by the single
network server. not least the quality of the cable used. One of the jobs of the server is to control
access to the files held on a hard disk.Hardware and Software
Network Basics. called a network
card.

Ring network
In a ring network the two ends of the bus are joined up.
1.
known as a bus.Network Topologies
There are a number of ways that the machines on a network can be connected together. the network
will continue to operate because the messages can go in the other direction. the disadvantage is that a single
break in the cable will stop all communications in the network. However. Bus network
In a bus network the hardware items all use the same. The advantage is that the installation of the system is comparatively easy
because there is only one communication line.
. central.
The shape of the network is known as its topology. This creates a loop so that data
can be sent in both directions along the cable. communication line.
2. If there is a break in the cable. We are interested in three different
network topologies.

usually the network server.
The wiring up of the network can be very complex.3. though. Star network
Network
server
In a star network the individual pieces of hardware are connected to some central point. This means that the failure of a single piece of hardware or
the breaking of a connector can only effect that piece of hardware and none of the others.
.

Device1
0
1
1
0
1
1
0
1
Device 2
This type of data transfer is called PARALLEL transmission. the speed of transmission is slow. As there is only one wire. because then a whole byte can be sent at once
instead of having to send one bit at a time. A
sensible number of wires would be 8.
. one signal for each bit.1 Different Types of Data Transmission
Serial and Parallel transmission of data
Data needs to be transmitted between devices in a computer system. Parallel transmission of data
is obviously faster than serial because all the bits are travelling at the same time.
If the devices are connected by more than one wire. then more bits can be sent at once.1. but
because of the fine tolerances in the transmission. This is known as SERIAL transmission of data.
Serial transmission has the advantages of being simple and reliable because the next bit is
not transmitted until the current one has arrived at its destination. so an 8 bit byte. that stands for a single character.
Device 1
011 0 1
1
Device 2
0 1
The diagram shows the data byte 01101101 being transmitted. because only
one bit can be transmitted at a time. However. Data is transmitted in the form of
bits down the wire. it is less reliable as the bits can become
muddled up.
only one bit can be transmitted at a time. will be transmitted
in 8 parts. The easy way to do
this is by using a single wire that links the two devices.5.

there are three different modes of
transmission possible. When data can pass in both directions at the same time it is known as
DUPLEX transmission of data.
Device 1
Device 2
.
If data is to be transmitted between devices .
a) Simplex mode.
Transmitter
Receiver
b) Duplex mode. but there is no way to send data in the other
direction. If data can only travel in one direction then it is known as a SIMPLEX
transmission. When data can pass in both directions. A good example of a simplex transmission of data is teletext information
which is passed to a television receiver.Modes of Transmission. but only in one direction at a
time. An example of half duplex is a CB
radio system in which each handset can either be set to receive mode or send mode.
Device 1
Device 2
c) Half duplex mode. the transmission is called HALF DUPLEX. An example of duplex transmission would be a telephone
conversation as both users can speak and be heard at the same time.

on the internet. The units
used to measure the bit rate are BAUD. it is important to limit the amount of data
that needs to be sent or the time it takes to download the data can be unreasonably long. 1 baud = 1 bit per second. One choice is to have as much detail as possible and
accept that it will take a long time to transmit it. the better the picture will be.
The data can be limited by such simple things as reducing the size of pictures so that they
only take up a small part of the screen. so a decision needs to be made.g. Remember that the more pixels that there are and the
more colours that can be represented.
Note that text can be sent much more quickly than other forms of information because it
needs far fewer bits (1 byte per character) than other types of data.Bit Rates
Information needs to be sent to devices in a computer system from other devices.
The number of bits that can be sent in one second is known as the BIT RATE. or that they are restricted to a few colours. e. This will be studied in more detail in the second year of
the course. meaning that there is less information to send so that the message will be sent
more quickly. For
example. However there is a
limit to the amount of information that can be transmitted in a given time down the phone
line. The other is to limit the resolution of the
picture. When data other than
text is being transmitted.
Speeding up the transmission of the information by reducing the amount of data that is
sent is known as compression.
. a picture stored in the memory of the computer needs to be sent down a
telephone line to another computer.

Error checking and correcting
When data, of whatever type, is being transmitted from one part of a computer system to
another, it is transmitted as a series of binary digits. Any data that is transmitted is going
to be made up of a very large number of bits. Consequently, there are bound to be
occasions when the data is not transmitted correctly. Luckily there are only two possible
mistakes that can occur, either a 1 is received as a 0, or a 0 is received as a 1. Mistakes
occur rarely, but when they do occur they can be very serious, as the information is no
longer correct. This makes it very important that there should be methods for checking
the data when it has been transmitted.
a) Echoing Back. The simplest way of checking the transfer of the data is to send it back
again. If the data that is sent back is the same as the data that was sent in the first place
then the original data must have reached its destination correctly, if not then it needs to be
sent again. This is known as ECHOING BACK. Echoing back is very effective, but
suffers from having to send data twice, thus taking longer than necessary, and needing to
be a duplex, or half duplex, system to allow data transfer in both directions.
b) Parity. All data is transmitted as bits (0s and 1s). The Number of 1s in a byte must
always be either an odd number or an even number. If two devices that are
communicating data decide that there will always be an odd number of 1s, then if a byte
is received that has an even number of 1s, an error must have occurred. E.g. the byte
01011000 has 3 ones in it. 3 is an odd number, so it fits the rule that it must have an odd
number of ones. When it is sent there is an error in transmission so that the first bit is
received as a one. So, the byte received is 11011000. This has 4 ones in it, which is an
even number, so there must be an error. The receiving device would ask for it to be sent
again.
Notes:
 If two mistakes are made in the same byte they will cancel each other out and the
faulty data will be accepted. This problem can be overcome, and in the same way, a
clever way of correcting error mistakes can be implemented. This method is not part
of this course.
 Earlier in this course it was said that a byte was the number of bits necessary to hold a
character code. Specifically, an ASCII character uses 8 bits in a byte, giving 256
different characters. This is not true because one of the bits has to be reserved for a
parity bit, the bit that can change to make sure that the number of ones is always odd.
This means that there are 128 different characters possible.
 The implication in all the above work is that odd parity is always used. Even parity
can equally well be used, whichever has been agreed between the two devices.
 Parity is not only used during data transfer between devices, but also when data is
transferred between different parts of the CPU.
c) Check Sum. Data will normally be sent from one place to another as a block of bytes
rather than as individual bytes. The computer can add numbers together without any
trouble, so another checking procedure is to add all the bytes together that are being sent
in the block of data. The carry, out of the byte, is not taken into account, so the answer is

an 8 bit number, just like the bytes. This answer is calculated before the data is sent, and
then calculated again when it is received, and if there are no errors in the transmission,
the two answers will match.

1.5.2 Switching
When a message is being sent from one machine to another, particularly over a wide area
network, the message may have to pass through other machines first. This may be forced
on the system because there is no direct route from one machine to another.
B
A

C
D

E

In the network shown, it would be easy to send a message from A to D or from A to B
because A is directly connected to both of them. However, sending a message from A to
C is much more difficult because there is no direct route. There are two ways that the
message can be sent
a) Packet switching. The message is split into a number of equal sized packets. Each
packet has a label saying where it is meant to be going and what number packet it is.
These packets are sent along communication lines towards the destination. Each time a
packet reaches a node on the network the node decides which direction to send it on. So,
one packet in the message from A reaches node D. The obvious route to take is the one
directly to C, but it is already in use for another message, so D decides to send it to E
instead. The next packet arrives at D and, this time, the line to C is free, so the packet is
sent direct to C. When the message has all arrived at C it has to be reassembled in the
correct order.
b) Circuit switching. Before the message is sent, the network reserves a route from A to
C. The message can then be sent directly from A to C and will not need to be reassembled
when it gets there.
Packet switching allows optimum use of the connections around the network because as
many routes are in use at one time as possible, whereas circuit switching means that the
whole message is kept together so it does not need to be reassembled at the destination.

1.5.3 Protocols
When data is being transferred from one place to another in a computer system there
must be rules set up as to how the transfer is going to be done. Typical rules would be
 A rule about the wire connecting the two parts of the system. Errors would occur if
one device had a serial connection and the other was expecting a parallel connection
 If one device sent data at a particular bit rate and the other device read what it
received at a different rate, the message would never be received correctly.
 If one device used even parity and the other device used odd then no correctly sent
byte of information would ever be accepted.
The set of rules that needs to be set up to allow the transfer of data to be carried out is
known as a protocol. There are a number of protocols that you may have heard of e.g.
http, tcp(ip) but don’t worry about them, you do not need to know specific examples of
protocols, but you should be able to discuss some of the rules that go to make up a
particular protocol.

1.5.4 Layering of Interfaces
The interface between two devices is the connection between them through which the
data can be sent.
This connection between the devices can take the form of the physical connection,
whether wires are used or some other form of connecting them together. However, it also
includes many other things like how error correction is going to be carried out, how
messages are routed from one place to another, how the flow of data is going to be
controlled, how the data transfer can be synchronised so that data does not become mixed
up, and many other things that need to be agreed upon.
This is a very complicated idea, but, in essence, there are two ways of setting up this
interface. One way is to try to do the whole thing in one go, and the other way is to divide
the interface into sections and do one bit at a time. For instance, first set up the rules
about how the devices are to be connected physically, and later on worry about how to
spot errors that have been made in the data transfer. This is known as layering the
interface because the most basic layer has to be done first and then more layers may be
put on top.
The main advantage of layering the interface is that changes may be made to one layer
without having to change them all. It also allows manufacturers to develop devices for
particular layers, knowing that they will be compatible with other devices at that level.

Advantages and Disadvantages of Networking
Advantages.
 The main advantage of linking computers in a network is that they can share data. If
two computers each have their own copy of a database then, unless no changes can be
made to it, one computer will always have a more up to date version than the other
because a change made on one machine will not register on the copy of the database
on the other machine. If the two machines are networked there only needs to be one
copy of the database, therefore any change made to the database will be used by both
machines.
 The machines can be used to communicate, a good example being the use of e-mail
over the internet.
 On a LAN the sharing of hardware and software between machines can reduce the
cost of a large amount of computer equipment being needed in a small area, although,
the saving on software is not necessarily what might be thought because the license
for network software is far more than for a single machine.
 Also on a LAN, access to files does not depend upon the physical location of the user,
but on who the user is. For example, in a school classroom, if a pupil was working at
a particular machine at the end of one lesson they do not have to use the same
machine the next lesson, they may even be in another room.
Disadvantages.
 The fact that the network allows access to user files from more than one machine
means that keeping files secure is far more difficult. Methods like user ID and
password systems have to be employed to ensure that the correct users are given
access to the correct files.
 If there is a fault on the network it can effect more than one station, and if the server
is faulty the whole network will fail.

e.
(2)
A.
(3)
A. so a brief explanation on first mention is generally a good idea.
a) State three pieces of hardware that are needed to create a LAN from a set of stand
alone computers.
By drawing a diagram. may have spurs to single
machines
-Server as part of network
-Sensible peripheral devices shown
-Advantage: If cable is damaged the network can continue to operate. with a LAN
typically being hard wired and a WAN being connected by using phone lines. while in a
LAN the computers are close to each other.
(3)
b) Explain why the communication over a WAN differs from that across a LAN and
state how the hardware necessary for communication would differ from that used in
part (a).
Two mark points available. these sets of initials are stated in the syllabus so
there is no problem in using them without explanation. describe a ring network and state an advantage
that a ring network has over a bus network.g.
Notes: The use of the terms LAN and WAN are perfectly acceptable without
reference to what they stand for. -Single ring of network cable shown clearly on diagram. modem and a telephone line. Be very careful about saying the same thing twice and
thinking you have both marks where you have really only said one thing.
(3)
A. Another
example of this is when a question asks for advantages and disadvantages of two
things. use that method unless you are totally stuck.Example Questions
1. note that they are not given for saying that the WAN is
remote while the LAN is confined to a small area. as it has been stated in the question. but that will be the easiest method. However.
.
2. be careful when
using acronyms like this as what might be obvious to you may not have been heard
of by the examiner. or otherwise.
Explain the difference between a wide area network (WAN) and a local area
network(LAN). This is really the same thing said
the other way around.a)-Network cards in each of the computers
-Cable to carry the signals from one point to another on the network
-A network server to control access to peripheral devices and to files on the shared
hard drive. -In a WAN the computers on the network are remote from each other.
b)-The distances between the computers are further than on a LAN…
-The cable used to connect up a LAN will only transfer signals over limited
distances
-Other communication medium needed.
3. The same thing given as an advantage of one will not be given a second
mark as the disadvantage of another. Even if it
hadn’t been stated in the question.
-The method of communication between nodes is likely to be different. There are
no marks for doing so.
Notes: If the question suggests drawing a diagram it is because that is the best way
of answering the question.

Explain the difference between
(i) simplex
(ii) half duplex
(iii) duplex
transmission of data.
(ii) –Half duplex is a means of transmitting data in both directions.
-An example of half duplex transmission is a walkie talkie where the handset needs
to be set to either send or receive. However.4.
(6)
A. As with so many of
these questions. in principle this answer is true.
01001101
10001000
10101011
00011011
An automatic checking technique is used to check that the data has been transmitted
without error. while a colour
picture of alternating stripes of red and blue would not need a lot of data to describe
it. at the same time.
Notes: This answer is not quite right because it is possible to imagine a page of text
written in 2 point font which would use a large amount of data. and.
The following bytes of data are received by one device after being transmitted from
another. than it is when sending a page of text. standard.
(3)
b) Explain why it is possible that a byte of data could still be incorrect despite passing
the test that you used in part (a). giving an example of the use of each. -Colour picture requires more data because each pixel must be defined
-Page of text has less data because each character is defined by its own byte of data
-Bit rate is the speed at which a given amount of data can be transmitted which is
more important the more data that there is. but only in one
direction at a time.
Explain why the bit rate is more important when sending a colour picture from one
device to another. if you try to make up your own examples you could be making a
big mistake. explaining how you arrived at your
answer.
considering there are only three marks.
(iii) –Duplex transmission of data is the ability to send messages over the same link. question requiring a standard answer. there is no signal sent back.
a) State which byte has been received incorrectly.
5. any attempts to complicate the answer must
be counter productive. (i) –Simplex is the transmission of data in only one direction
-An example is the transmission of a television picture from the transmitter to the
receiving aerial.
6.
(3)
A.
(1)
.
Notes: Nice. Also this answer does not take any account of compression algorithms that many
students may know something about.
in both directions.
-An example is the use of a telephone.

a)-10101011
-Bytes should pass a parity check
-Other bytes are of even parity while this is odd
b) -If two bits in the same byte are in error the effect of each will cancel out the other. In order for the
data to be transmitted and received properly a protocol must be set up between the
two pieces of hardware. a) Explain the term “layered interface” when describing intercommunication between
devices.
-Parity type
-because if the computer transmits using odd parity and the printer checks using
even parity correct bytes will never be accepted. on sight of the
word protocol. It
would be difficult to think of a question. -Packet switching sends message in equally sized pieces in any order. while circuit switching requires a route to be
established before transmission. desperately want to write down TCP(IP) or http. and hence is
only worth one mark. stay with the ones in
the text then there is no chance of misunderstanding.
. This is the same point from two perspectives. You may know
more than the ones stated in the text of this chapter.
7.
8.
9. be warned. Be very careful. Packet switching does not need
a route to be established. The immediate reaction is to say that circuit switching
needs a route to be established before transmission.
Explain the difference between packet switching and circuit switching.
Notes: There are many possible answers to this type of question.
Notes: A difficult question. while in
circuit switching the message is sent in order meaning that it does not need to be
reassembled at destination.A. (1)
A.
-Packet switching involves the individual packets being sent onto the network
before a route is established. -Baud rate
-necessary because if the computer transmits at a different speed to that which the
printer can receive the message will become jumbled.
(4)
A.
(2)
A. for instance the physical connection between
devices and the agreement of error trapping routines will be handled separately
b) -The rules in one layer can be altered without having to alter those in other layers.
(2)
b) State a reason for arranging the interface between devices in a layered fashion. at this level.
A computer is to use a printer to provide hardcopy output of jobs. which could possibly have
those as answers. State two parts of the protocol which would be essential in
this example. The second mark is much more difficult to find.a)-Different rules have to be established to allow the communication to take place
-These rules are split up into types. giving reasons why they are necessary. Some students.

a)-Hardware can be shared.
A school computer department has decided to invest in new hardware in the two
rooms that it uses for computer lessons in the school.
a) State four advantages in implementing the network solution.
-Communication can be carried out between machines in the two rooms.
b) -Files are less secure because of reliance on single drive
-regular back up copies of files should be taken. they do not have to
use a particular machine. so all machines can
access the same information in common files.
(2)
A.
.
-Software can be shared.
-Files stored on the disk drive only need to be updated once. There is no need for a printer for each machine.
-Privacy of files is more difficult to control because of common access to hardware
-Use of passwords to control access to files. Only one copy of each piece of software is required.10.
(4)
b) State a disadvantage of using a network in this context and suggest a solution to the
problem.
The teacher in charge has to decide between a network of computers or a collection
of stand alone machines. The teacher has asked your advice about which hardware
to implement.
-Pupils can access their files from any machine on the network.

during the training of the staff. one of the input operators proves to be colour
blind then the input screens may need to be altered in order to not have any clashes
between red and green.
System Lifecycle as an Iterative Process
When considering the systems development life cycle it is important to think of the
different stages as a continually developing process rather than each stage being an end in
itself.1. If.
This reliance of each stage being on the following stages as well as the previous ones
means that the process is said to be iterative.6 Systems Development Life Cycle. If the problem definition agreed with the end user
later proves to be impossible to implement then the problem will have to be redefined.
When one of the stages is completed the following stages may mean that the previous
ones may need to be considered again.
. If
the required input proves to be not feasible then it may be necessary to alter the expected
output.

The owner of the problem will be happy if the
analyst can introduce a computer solution. This
is the systems analyst. “Do the 5 questions”.
. If you are asked to answer questions 1 to 5
and you do 6 to 10 instead there is an obvious breakdown in communication. The problem arises when the analyst.
It seems obvious that if someone is doing something for someone else that they should
make sure that they know what is required. but does not understand the
consequences of using computers to try to solve the problem. that decides that a task
would benefit from computerisation. Unfortunately. and then for a list of objectives to be written up. whether such a
solution is even possible. solves the problem that they think needs
solving.6. or a company or organisation. For this reason it is necessary for the organisation to employ a
specialist who does understand computers and computerised solutions to problems. it is probable that the systems analyst is not expert
in the area of the problem. the owner of the
problem probably understands the problem itself quite well.
There will normally be a person. while the owner of the problem expects a very different problem to be solved. but this is
what can happen if you only listen to the instruction.
The system analyst’s job is to solve the problem by planning and overseeing the
introduction of computer technologies. This list of objectives. Unfortunately. This belief normally arises because there is a
problem which cannot be solved by previously used methods or similar problems seem
to have been solved by computerisation elsewhere.
if they are all solved.1. The different people involved
then agree to the list of the objectives and the success or otherwise of the project depends
on the completion of those objectives.1 Problem Definition
It is important from the outset to ensure that when a computer system is being designed
all those that are involved are agreed about the aims of the system. indeed. or. The method
most often used to overcome this problem is for there to be discussions between all the
interested parties. will be the solution to the problem.
The definition of the problem is the most important part of the analysis because if it is not
done correctly the wrong problem may be solved. who
doesn’t know very much about the business.

If there are no workers with the necessary skills
then the computerisation is not feasible.
 What is the effect on the human beings involved? If the car plant is the only major
employer in the region. if it is not possible to manufacture a robot arm of the correct
dimensions to fit into the small areas under a car bonnet.
 What effect will there be on the customer? If the customer is likely to be impressed
with the introduction of the new systems then it may be worth the expense.
a decision must be made about the value of continuing with the computerised solution. certainly the
Government would.
When the organisation and the systems analyst have agreed the definition of the problem.6.
 Is the solution economic to run? It has been decided that there are tremendous
benefits in producing a robot production line and the robots are very cheap to buy. from a number
of points of view. however. However. the next
stage will be for the analyst to collect as much information about the process as possible. then the employer may decide that the human cost is too great. but
they have so many electric motors.
The feasibility study will consider the problem. will
the introduction of robots increase the profits made by the firm?
If the feasibility study shows a positive result which is accepted by the company. the systems analyst is being
paid to look at the problem. it would simply
not be feasible.
The organisation may be convinced that there is a problem to be solved. what is the point?
 Will the introduction of the new systems be economically beneficial? Put bluntly.
 Is the workforce skilled enough? It will be necessary to employ highly skilled
technicians to look after the robots. and the proposed solution. and that its
solution will be worth the effort and the expense. from another point of view.1. and the introduction will put much of the workforce out of
work.
.
 Is the solution economic to produce? Perhaps the robots exist that can be programmed
to assemble this engine and the benefits will be worthwhile. if the cost of
the robots and the program to control them is so great that it puts the car manufacturer
out of business. The analyst is an
expert in computer systems and what is possible with computer systems.
This report is called the feasibility study because it says whether the solution is feasible. it doesn’t matter how big an
improvement there would be in the quality of the finished product. However. However. and they are so slow at assembling the engines
that it is cheaper to employ people to do the job.2 Feasibility Study.
if the customer will notice no difference. the introduction of the robots is not feasible. and its solution.
 Is the solution technically possible? A car firm may decide that if robots are used on
the production line to assemble the different parts of engines then quality of work
may improve. This analyst
must consider the problem from the point of view of the computerised part of the solution
and make a report to the organisation saying whether the solution is possible and sensible.

1.6.3 Information Requirements of a System and Fact Finding
When a computer system is being designed it is necessary to ensure that the designer of
the system finds out as much as possible about the requirements of the system. We have
already mentioned the importance of defining the problem but further difficulties can
arise. Imagine an organisation that commissions an analyst to design a new payroll
program. The analyst and the boss of the organisation agree that the software needs to be
able to communicate with the relevant banks, and to deduct tax at source and other
important details. The analyst designs the solution and the software is written. It is the
best payroll program ever produced and is installed into the computer system ready to do
the first monthly payroll. Unfortunately, many of the workforce are employed on a
weekly basis. A simple question to one of those paid in this way would have highlighted
this for the analyst and meant that the costly mistake was avoided. When a system’s
requirements are being studied there is no room for errors caused by lack of information.
The feasibility study has been accepted so the analyst now needs to collect as much
information as possible. Obvious methods of collecting information are to ask different
types of people. It may not be feasible to ask everyone in the organisation for their views,
but a representative sample of workers, management, customers should be given the
chance to supply information. After all, the part time worker on the production line
probably knows more about the business than the analyst. There are three accepted
methods of finding out people’s views:
1. By interview. Interviews are particularly important because they allow the interviewee
to talk at length, and also to leave a prepared script. However, they are very time
consuming and consequently restricting in the number of people whose views can be
sought.
2. By using questionnaires. Questionnaires make it possible to find out the views of a
large number of people very quickly, but because the questions are pre-determined the
person who is supplying the answers may find difficulty in putting their point of view
across.
3. A compromise is to hold a group meeting. This allows a number of people to discuss
points and make their views known and yet cuts down on the amount of time spent in
interviews getting the same answers over and over again. The problem with meetings is
that one or two people tend to dominate, not allowing all the members of the group to
give their opinions.
Often the views of the people connected with the problem are clouded by years of
familiarity, so it is important for the analyst to also gain first hand knowledge of any
existing systems. One way to do this is to observe the current system in action. Care must
be taken to take into account the fact that if the workers know that they are being
observed it is unlikely that they will behave in their normal manner. This is the same
effect as a television camera has on otherwise fairly sensible individuals. The second
method is to collect printed documentation and study it in order to find out what data is
required by the system and what form information is output.

1.6.4 Requirements Specifications
The planning of any system design must start by deciding what the requirements are of
the system. A system may need to store data for future reference or processing. However,
simply being aware that the system may need to store data is not enough.
 Decisions need to be made about the types of data to be held as this will dictate the
form that the data will be stored in and the amount of storage space required for each
set of information.
 Calculations as to the number of sets of data that are going to be held have to be made
because the volume of storage will make some storage devices more sensible than
others. Also, the volume of storage can effect the structures that will be used to store
the data.
 Decisions need to be made about the relative importance of the different ways of
accessing the data. Is it going to be necessary to access individual items of data or
will all the data be accessed at the same time?
 Will the data be changed regularly or is it fairly static?
When decisions are made as to the direction that a particular system is going to take, it is
normal to produce a list of tasks that need to be carried out to complete the system. These
tasks should be in a specific order. It would not make sense to consider inputting data into
the system before designing the data structure into which the data is to be put. This list is
called a priority list and it forms the basis of the system design. Each of the tasks that are
in the list should then be considered separately to decide the important points about each
one. An example would be that the file of information on stock being held in a business
must allow
 for 1000 items (immediately putting a lower limit on the size of appropriate storage)
 for direct searching for information on a single item (means that some storage media
are not suitable, and that some data structures cannot be used)
 another file, of manufacturers, to be accessed from each record in the stock file to
facilitate reordering (forces one field to act as a link between the two files).
Plenty of other facts must be considered and decisions made, but a set of constraints has
already been placed on the design. This is known as the design specification and it should
be agreed between the analyst and the organisation before the design is implemented.
Often, the inputs and outputs to a system and the storage and processing that goes on in
the system is such that, in order to understand it, the system needs to be divided up into a
number of interconnected sections, or modules, each one being simple enough to be
handled as an entity. A diagram can be drawn which shows all the sections and how they
fit together. Such a diagram is called a Jackson diagram.

Jackson diagrams:
A Jackson diagram starts with the original problem as the highest level. The next, and
subsequent, levels show how the problems in the previous levels are split up to form
smaller, more manageable, problems. This continues until each of the blocks in the lowest
levels are self contained, easily solvable problems. These individual problems can then be
solved and combined according to the links that have been used. If the links between the
different blocks are then used correctly, the result will be a solution to the original
problem. Imagine a Jackson diagram as a method for showing the individual modules that
go to make up a solution to a problem and the relationships between them.
Original Problem
Links
Individual modules
Final level
The links between the modules can be conditional. For example if the result of a module
was a mark out of 100, then there could be two possible print routines, one for failure if
the mark was below a certain level, and one for pass if it was above the pass mark.
An example of a Jackson diagram to show the solution to a simple problem.
A register is taken of the 25 students in a class. Each student can be either present or
absent. It is necessary to print out the number of students who are present and the number
absent.
Register

Initialise

While count
<25
*

Count = 0
Cpresent = 0
Cabsent=0

Input
Present or
absent
Increment
Cpresent

*
repeat

Output

Output
Cpresent
Cabsent
Increment
Cabsent

As the name implies. Data
flow diagrams can have complex shapes for the boxes that are used. Rectangular boxes. storage. rather the logical train of thought that has been used
to produce the diagram. but the important
thing is not the shapes of the boxes. and the software characteristics that will need to be
satisfied for the system to operate. indeed. Such diagrams are intended to show
how the processes and the data interrelate. not the details of any of the programming
logic.
Note: A Systems Flowchart is another name for a data flow diagram.
At this stage the analyst will also identify the hardware that will be necessary for the
system to operate as the user requires.Data flow diagrams:
These are diagrams that are used to describe systems. are perfectly
acceptable for all elements in a data flow diagram. Boxes are used to stand for input.
processes. and output. Arrows show the direction of communication around the
system. these diagrams are
used to show the directions of flow of data from one part of a system to another.
. though not always used. and communications outside the system.
Students are expected to be able to follow the logic in a data flow diagram and. but not under examination conditions because the drawing of such a
diagram would take too much of the time allowed for the exam.
produce their own.

The main task in input design is to design the interface with the outside world
so that data can be passed to the system. The way that the data is input to the system depends on a
number of factors. so choosing
these colours to stand for information that is dangerously near a limit or at a safe
level. colour combinations have to be chosen
carefully.
. both software and hardware.c which covered the different forms of software
interface. the
experience of the operator.
Output Design.
The results that are produced by the system must be presented in a way that is appropriate
for the application. could be disastrously wrong.
or is there an automatic way to enter the data?
 The experience of the operator. the hardware available. Similarly. as is
yellow writing in some lighting conditions.
 The design of the user interface. Output. Blue writing on a black background is almost impossible to see. In
order for users to be able to understand the information presented various tricks can be
used.6. namely. If the system is designed to produce bank statements for customers. indeed.5 Design of Input.2. Is it graphical/textual/physical in nature? Is the data already
in existence or does it need to be collected first?
 The hardware that is available. Is the data to be entered via a keyboard by an operator.
Diagrammatic depiction of the system processing is covered in section 1. is the danger of providing too much.
This section relates back to section 1.
 The data that is required.1. a burglar alarm system
would not serve the purpose for which it had been designed if the output is a message on
a computer screen saying that someone has broken in as there is probably no-one in the
house to read it. but students should be aware
that they exist.
Equally important to giving enough information. the form that the output needs to be in.
 Information can be arranged on a monitor screen by always putting the same sort of
information in the same place.
 Information can be colour coded. which is why the alarm was needed in the first place.7. and Data Structures
Input Design
All systems require input.
It is also necessary to be very careful about choice of colours. Notice that this implies some form of decision
making on the part of the processor to determine what is important in the first place. People who are colour
blind commonly find difficulty distinguishing between red and green.e. whether there will be an operator present.
The decision about the type of output will depend greatly upon the same factors as the
input. The operator will then quickly become accustomed to
the relative importance of different areas of the screen.
then it would not be sensible to have an audio output. Important information may appear in red while that
which is less important is in black. Similarly. above. It is
not necessary to go into great detail about such diagrams.

queue. were described.
Data structure design. Questions on this part of the syllabus will tend to ask for
the sort of choices that need to be made rather than any complex analysis of fitting a data
structure to a given situation. In section
1. stack.4.
. What is important is getting it back again when it is needed.
This is when the normal writing on the screen is black on a white background.
The data used in a computer solution will need to be stored somewhere.
A printer may be reserved for special messages so that a hard copy of the information
is preserved. though simple examples like modelling a queue at a check
out till may be asked. anything that
makes the operator’s eye go to that part of the screen. Again. The storage is
not that important.



Video reversal can be used to highlight a particular piece of information effectively.
Very important pieces of information may be shown as a dialogue box obscuring the
rest of the screen until it is dealt with.
Information can be made to flash. the fact that the information appears on that printer means that it
has a particular importance. or can be printed in a different size. When the solution
is designed it is necessary to decide how access to the data will be handled and to choose
an appropriate data structure. the data structures array. but the
piece that needs to stand out is shown as white on a black background. linked list.

is of
paramount importance. radio controlled. that the finished system must match. does it do what it is meant to? This question
can only be answered if it is known what the system was meant to do in the first place.System Evaluation
Any system must match certain criteria if it is to be considered successful.
.
only to find that it is 30 cms long when delivered. car fits all these criteria. This does not
only apply to a computer system but any system. A toy. However.
There would be many other facts which would have to be true before most of us would
recognise that this system is a car. or should there be a new criteria that gives a minimum size for the vehicle. In other words. a car must satisfy various
criteria before being able to be called a car
 it must move under its own power
 it must be possible to steer it
 it must have 3 or 4 wheels
 it must have seats. this list of criteria. It must also be agreed between the designer of the system and the
commissioner of the design. When
systems are being designed. Perhaps the
second bullet point should have specified that it has to be controlled from within the car
itself. so that there will be no unfortunate misunderstandings. but it
was not the sort of system that we had in mind when designing the criteria. We
can imagine a situation where the Ford motor company commission a new car design. For example.
Note that these criteria are decided before the system is created. They are used to decide
how well the system works. some assumptions have been made in just
the four criteria mentioned here.

Indeed. the coded program
itself.f. Indeed.7. These algorithms may well be in the form of flow diagrams or
pseudo code. This type of documentation is not intended to be accessible
to the user of the system. anything that will aid a technician in
maintaining or updating a system.
Requirements specification
This is a list of the requirements of the customer for whom the system is being designed.
Documentation is created at different stages in the life of a system and for different
people to use. one part of a solution
may be the production of a file of data. and details of any
library routines to be used will also be in the program specification. details of hardware configurations. how it should be used. The ways that this file of data relates to the other
parts of the system. who does not need any of these details to be able to use the
system correctly.
It consists.
and also the criteria for each stage of the solution. It is usual for the system analyst and the
customer to sign the list of requirements so that there is no confusion when the work is
finished.Documentation
The documentation of a system consists of all the text and graphics that explain how the
system was produced. This will include the
different stages. and the specification of the file (what is the key field? How many
records will there be? What type of medium should it be stored on?) make up the design
specification.
Design specification
Taking the requirements specification and working out the stages necessary to produce
the required end product is known as the design specification. the data structures necessary. of the criteria that will be used for the evaluation of the finished
system that were discussed in section 1. For example.
Technical documentation
The technical documentation will include the program specifications. largely. technical documentation is otherwise known as
maintenance documentation.
. much of the project work that is
done in module 4 consists of producing the documentation for a problem solution. often shown in diagrammatic form as mentioned earlier in this chapter. and how it can be maintained. The language to be used. Generally. Some of the different types of documentation are met in this section and
others will be encountered later in the course.
Program specifications
These will include detailed algorithms showing the method of solution for some of the
parts of the problem.

This type of documentation is called on-screen help.User documentation
This is the documentation for the person who will actually be using the system. Items
normally included in the user documentation will be
 examples of output screens
 examples of valid input
 methods of input of data
 error messages and what to do when they appear
 How to install the system onto specific hardware
Some user documentation is part of the software and can be called up onto the screen
when it is needed.
. It
contains those details that are needed to make the system operate as it should.

8. The old system is removed and the new system replaces it
completely and immediately.
When the system has been completed it has to be implemented so that it is performing the
tasks for which it was designed.1.
The system handover. Initially. This allows results to be
compared to ensure that there is no problem with the new system. Such a system is
‘safe’ and also allows staff training to be carried out. This is a compromise with the idea of
parallel running.
This topic is not fully expounded upon here. itself can be done in a number of ways:
 Parallel running. this involves
 ensuring that the correct hardware is available
 arranging for staff to be trained in the use of the new system
 inputting the data to the data files. the system. the candidate simply needing to understand
that there are different methods of implementation and be able to outline some of the
methods along the lines shown here.
 Pilot running. but it does not give a clear idea of the effects on the system of the
large amounts of data that are going to be encountered in the full application.
 Phasing.g.e. either manually or by downloading them from the
original system.3. but it is obviously very
expensive because of the need to do everything twice. This topic will reappear for a fuller treatment in
section 3.
Specific types of testing have already been covered in 1. Parts of a system are replaced while the remaining parts are covered by the
old system. Key parts of the new system are run alongside the old system until it is
considered that they have been fully tested. but also allows for a back-up position if the new version does
not work as anticipated.6 Testing and Implementation Planning
Any system needs to be tested to ensure that it works.
 Big bang. or direct change. Until the system can be considered fault free. but in reality such testing is impossible in all but the simplest of systems
because it simply is not possible to test every conceivable input to. This difficulty means that testing that is to be done must be carefully
planned and that it should relate directly to the criteria referred to earlier in this chapter. the old and new
systems are run side by side. and for staff
training to take place. This seems to be a fairly obvious
statement. This allows for some testing of the new system to be done. or logical construction
in. Parallel running is used in
situations where the data is so valuable that there must be no possibility of failure. both doing the same processing.
.6.

For many reasons the original system may no longer be satisfactory. the law governing a system
may change. new ideas. One
solution would be to produce a totally new system.
While the system is running it will need attention because of faults being discovered. However. a system should never be considered to be finished. another would be to adapt the present
one so that it can be used in the new circumstances. Rather than being a
linear process with a beginning. this
again needs a technician with a set of maintenance documentation. continually returning to previous stages to fine tune them and take advantage of
changing circumstances.
Computing and computer applications is a subject that changes so regularly through
improvements in technology. the original reasons for a particular
system to be created may change.
that. This situation is reviewing the system
and is the main reason for technical documentation.1. hence
they would be considered successful. the hardware may alter.
. in reality. a middle and an end.8 System Maintenance and the Software Life Span
Systems may be designed for a well defined purpose and may realise that purpose.6. it should be thought of as a circular
process. different legal frameworks trying to keep pace.

Perhaps there is no freely available piece of software that will satisfy the needs of the
company.
. allowing.1. a decision has to be made about the software that should be used. for it to be written.
 Because the software will be in general use there are likely to be well established
training courses for the staff to be sent on to learn about the software.
 If it comes as part of a suite of software it can be relied upon to be compatible with
other applications. the import of data.
 Copies of the software have been in use for some time and will have been in use by a
variety of users. and. This implies that the
software will be considerably cheaper.
There are many pieces of software that have already been written and are immediately
available to buy. consequently it can be expected to work. This means that any bugs in the software should have been found and
rectified. for example.
A Custom package is one that has been specially written to solve a specific problem. This type of software is called ‘off-the-shelf’ software because you can
literally go into a computer shop and pick a copy off the shelf. therefore they share the
development costs rather than one having to foot the whole bill. does
not contain extra routines that will never be used.1 Custom Written and Off-the-Shelf Software. There are a number of
advantages in buying an off-the-shelf package:
 The software has already been written and so is immediately available rather than
having to wait.
 The software will be used by many people or organisations. equally importantly.
When the analyst has analysed the problem and come to a conclusion about how it can be
solved.7 Choosing Applications Software
1.7. sometimes a considerable time. A piece of custom software should mean that the organisation gets a piece of
software that will do all the things that it requires doing.

Features of Common Applications
Stock control. If the quantity in stock falls below a pre-determined limit then
the system should automatically institute a reordering process.
Many stock control systems are charged with the need to record the number or amount of
the goods that are in stock. which
obviously does not apply to the towels. Each record undergoes the
same type of processing.
The traditional picture of the payroll application is that the master file of workers is held
on a tape.. multiplying by the
hourly rate and then doing the tax calculations. the old files are
kept so that if the new versions are corrupted they can be reproduced using the old master
.
If the organisation is the one that is filling the order then the operation is similar. In this system. as is the transaction file that holds the workers’ details for that week.
Order processing. or where the goods are being stored in the shop/warehouse. whereas the information stored about
bulldozers stored by a plant hire firm would not include colour as it is irrelevant to their
function. The two
are arranged in the same order and then run together and the results stored on a new
master file. The third is to do
with the use of the goods. and the accounts
department are told that the order has arrived and that clearance has been given for
payment to take place. This gives rise to the ancestral filing system form of
backing up of files which was introduced in section 1.
There are typically three areas that need to be handled by a stock control program.
As the name implies. working out the number of hours worked. stock control systems are used to keep track of the stock being held
by an organisation.
Payroll.4. Copies of the orders would be
sent to the accounts department so that when the invoice for the goods comes in it can be
matched up with the order. The process requires no human
intervention during the processing. What would be included would be the horse power of the machines. The
first is to keep details of the individual items that the organisation holds in its stock. but in
reverse.
The payroll is a perfect example of a batch process. again held on a tape. the ordering system is
informed so that the live order can be shown to have been fulfilled. The second is to store information related to the
product though not directly about the product itself. A consignment of towels in the stock of a shop
will need to have the colour of the towels stored. Examples would be storing details of
the supplier. This would be done by
using the details of the supplier and possibly including the human management in the
process to allow for variations caused by season/fashion/. Who has hired the bulldozer out? Where is it? When is it due
back? What sort of condition was it in when it was hired out?
Stock control systems are all to do with keeping track of stock. All the records need to be processed
during the same run because all the workers need to be paid.
These details will differ dependent on the item being held and the information about it
that the organisation decides is important. recording stock levels and
the condition of the stock and keeping track of where it is going. When the goods are delivered.

Finally. It can be used to make predictions. or it may be a new traffic flow system around a
town.
This is simply the use of a computer system to design a commodity.9) and then
sent to the processor. This code is then validated (see chapter 1. When the record is found the contents of the record are used to produce a
printout for the customer (till receipt). and finally to arrange for payment. will the robot tool be able to manoeuvre into a position to be able to screw
the two halves together.
The identification of the goods can be done in a number of ways. The software can be used to do calculations. the file is likely to be held on a disk with an index to
allow fast access to individual records. The results of these decisions are actions that are carried out.
Marketing. The
computer receives information about the process from sensors which allow it to make
decisions. It may be a house.
what will happen if this street is made one way?
. This process is known as feedback. having decided on the design of
the carburettor the prices of the individual components can be used along with the known
costs of production to calculate the cost of each unit. The next set of
input from the sensors not only tells the system about the current state of the process but
also allows the computer to compare with the last set of inputs to decide whether the
actions that it took last time had any impact. Nowadays. Marketing is the term given to this process. and to accumulate the total value of all the goods
that have been bought. but the standard method
is to read a code from a barcode. In computer terms it would
include the use of systems to produce advertising literature.
When a product or service is developed it is important to make the potential customers
aware of it. the promotion of the product
on the world wide web and the use of techniques such as direct mailing by using
purchased files of people who may reasonably be expected to have some interest and then
mail merging to produce ‘junk mail’. or
a carburettor to fit a particular engine.
Point of Sale systems. The first is to identify
the goods being bought. The processor uses this barcode as the key field when searching the
product file.
As the name implies. will the roof be well enough supported
by walls made from that particular product? It can be used to make decisions about the
manufacture. the second is to carry out whatever processing is required and to
produce a satisfactory output. this is the use of a computer to automatically control a process.
Computer Aided Design (CAD). the payment can be made electronically by sending details
of the customer account to the bank or credit card company from where payment will be
made to the store immediately. this would imply that the records are overwritten
and that there is no new version of the master file created.
Process control.and transaction files. It can be used to cost a solution.
A computer used at a point of sale needs to carry out three actions.

If the two
principles of CAD and CAM are combined then it should be possible to produce a
seamless process whereby the computer produces the design which is electronically sent
to another system where the design is produced by a computer controlled robot.Computer Aided Manufacture (CAM).
CAM is the use of a computer to help with the manufacturing process.
.

Spreadsheets are a type of software that allows data to be stored.
the printout of which can be used directly as the starting point for a printing process. budgeting.
There is nothing frightening about this section. payroll
software would be used in a large scale application). more specialised. Examples would be
profit and loss accounts. The software
automatically divides itself into specific uses. If this were all that a
spreadsheet was to do then there would be other. A spreadsheet is particularly useful because it can store different types of data. The student should be able to isolate the
important characteristics of an application from the description and then decide which of
the generic software best fits the application characteristics. indeed any example that requires the
manipulation of figures to give accurate results or forecasts or predictions. proof copies of
books and magazines. and that it can perform calculations on the areas (cells) where
the numerical data is being stored. The software allows morphing from one
screen to another and also allows animation and full use of text and graphics within
.
Typically DTP software is used for the production of leaflets. payrolls (although other.7.
Spreadsheets. Many word processors now have features which previously would
only have been found in a DTP. posters.
This type of software is characterised by the ability to produce a page of printed output
that has been designed by using advanced layout techniques.1. and the distinction between a DTP package and a word
processor has become less clear cut. If a salesman is to do a presentation to a group of people it is now
possible for him to take a computer to the meeting with a previously prepared
presentation on it. for instance the ability to produce text in columns or to
surround graphics with text. more satisfactory types of software
available. The page may well contain
text. The software allows for the preparation of a show which typically
follows a storyboard of individual screens. tables and many other types of output each one of which may be better
produced using a word processor or a drawing package or a spreadsheet. mail merging. Spreadsheets should be considered for any example
where data is stored and calculations need to be carried out on it. Writing
letters. preparing text documents for use in other software packages. are all
typical uses of a word processing package. The value of the
DTP is that it contains powerful tools for arranging these individual items on the page.
Presentation software.2 Generic Applications Software.
Used for applications that have the need to communicate with others using text.
Word processing.
including numerical data. graphics.
Desktop publishing (DTP).
The growth of the use of presentation software has followed the development of portable
computer systems. The intention is simply that students
should be able to suggest sensible software for given applications.

The two most common are bitmap graphics where
each pixel is treated separately. and vector graphics where the lines on the drawing are
created mathematically. Different software packages create the graphics in different ways
for instance Paintbrush creates pictures in bitmap form while Draw uses vectors. a soundtrack can be added to complement the pictures
being shown.individual screens. This could be
accomplished using an over head projector linked to the computer or an RGB projector. The
simple way of describing the difference is in sizing the drawing. There are many different forms of graphics package split into groups dependent on
the way that the graphic is produced.
Drawing packages. or to a piece of presentation software for inclusion in a
display sequence.
. If a drawing stored using vector graphics is increased in size the only thing
that changes is the mathematical formulae for producing the lines. Ideally. Another use for such output is to enliven a page on the world wide
web. which will produce a
picture of comparable quality whatever the size. This would mean that a single
monitor would be fine for some automated display in a department store.
This is a package that produces graphics output. If a drawing held as a
bitmap is increased in size then each of the pixels is increased in size and hence becomes
more obvious. such a presentation should be output via some device that would be
designed for the audience expected to be watching. but would
require something more akin to a projection screen for a larger audience. Often such output is exported to a DTP
for inclusion in some publication. If required.

but would include many uses of control
software. but would
have other sections which would be for that warehousing system alone. the further away from the standard. designed for that
particular purpose. be
one-off.
. the software that would drive them would. the more difficult it is to use standard
software. A stock control system in a warehouse would have standard modules. Robots used on production lines tend to be one-off machines.Applications for which Common Packages are not appropriate
Common applications packages are those that have been designed to satisfy particular
needs that are common to a number of different applications. Uses that
would require such specialist software are legion. and the more likelihood there is that the system will require software written
specially for it. similarly. The important
consideration is how different from the standard design is the system for which we want
the software. consequently. There are many other
examples where computers are necessary but where the use is so specialised that the
software will need to be written (or at least tailored) for that particular use.

in which data can be placed. Letters or other documents are
perceived to be unacceptable if they contain an error. which can be
thought of as the direct precursor of the word processor.Purpose and Impact of Generic Software. the truth was far from this. most had little problem and even learned new skills making
them better qualified. In order to
do this the output device needs to be top quality otherwise the other parts of the system
are let down. The logic went along
the lines of: Each operator will be able to work much faster and hence produce more
output. whereas the facts are that the amount of paper
consumed in office applications has multiplied enormously.
and there were some typists who.
The impact of the different types of software have been profound.
Word processing.
A spreadsheet is essentially an area which can be split up into rows and columns forming
‘cells’. While this was true to some extent. particularly
calculations that make predictions about what would happen if some value were to be
changed.
Strictly speaking a DTP combines elements of software and output devices so that
published quality material can be produced from a desk top computer system. therefore some of the operators can be made redundant. In
. and the software needs to enable the user to combine graphics images and
textual images and manipulate them around the page before being printed out.
Desk Top Publisher (DTP). While this happened a
little. If an error is spotted then it is
corrected and the document is reprinted.
Spreadsheets. largely through being older found great difficulty in
changing their old practices. The advent of electronic machines was heralded
as the start of the paperless office. In its simplest form then.8. However. This
system compares with the system that used to be in operation of creating the page
physically from cold type and attaching the page to a commercial printer before printing
out multiple copies. spreadsheets begin to take on added significance when
formulae are applied to the numeric data in the sheet to make calculations. The first was because of the fear of unemployment. a spreadsheet is simply a
data storage system. and there are now more computer operators than there
ever were typists. giving more job satisfaction and the capacity for higher paid jobs.
The purposes of the different types of generic software were covered in section 1. The addition of a
language so that algorithms can be programmed makes a spreadsheet a very powerful
software tool which goes beyond simply juggling with figures necessary for doing a
payroll or keeping the accounts and makes it possible to model situations in mathematics
and the physical sciences. The second fear was that in order to use one of the new machines
typists would have to undergo considerable training. Spreadsheets can also be expected to have presentation tools like graphing
packages in order to produce the results in easily understandable form.c. The use of computers
running word processing programs was greeted with fear by most type writer operators
for two reasons.
Expectations have changed markedly since the days of the typewriter. Commercial printing presses are now electronically set up meaning
that the publication and the press can all be controlled from a single micro computer.

This has led to there being many
thousands of titles now available. perhaps. colour and colour change. This distracts
from the message that is being attempted to be put across to the audience.
Drawing packages are. No longer does the school worksheet need to be a simple text document. done little for the quality of
such titles. and the
production is very simple.
Presentation software allows someone to prepare a series of inter related slides to
accompany a talk that is being given.
. in this
context the syllabus is referring to the concept of the user being able to create graphics
which can then be imported into other software packages to enhance the work that is
being done.the 1970’s there were fewer than 200 magazine periodicals available in Britain because of
the difficulty of setting up a new publication and the cost which could only be
recuperated if there were sufficient sales of the magazine. but it is also true that no amount of clever gimmickry can hide a poor message. even photographs can be included. There is no
doubt that presentation software can be used to make a message more accessible to the
audience. the ability to morph into the next slide and many
other features. However. or even to be a stand alone system. software that allows the creation of graphics
using vector graphics as opposed to painting packages that use bitmaps. This leads to
presentations becoming overloaded with tricks in order to make an impact. Each slide has
animations.
Presentation Software. pictures. often a one person job. When such software was first available those who used it produced
presentations that were out of the ordinary and consequently it was seen as something to
aspire to because of the novelty factor being able to hold the attention of an audience. but
diagrams.
However. as the use of such presentations became more common. The cost of producing a
magazine has fallen so much that a small circulation title will still make a profit. strictly speaking.
Drawing Packages. it became necessary to
use more and more complex techniques to maintain the novelty factor. although it has.

Example Questions.
In the same scenario. It simply needs two statements of
fact. When making the decision to change.
Describe how CAD/CAM can be used to produce prototype designs in a
manufacturing process.
(4)
A. State two reasons why custom made software might be more
appropriate than off-the-shelf software. not just hard
facts. The office is likely to be a relatively small operation with few users. Also expected is a linking of the question to the scenario given.
3. (4)
A.
Discuss the reasons that a solicitors’ practice would have for choosing off-the –shelf
software rather than custom written software if it was decided to change the word
processor currently being used because it was perceived to be out of date.
2.
and four marks means four minutes to answer the question and with reading and
thinking time I’ve certainly used that up. Notice that
there is an indication in the number of marks for the question of the degree of depth
of the answer. There were plenty of other points that could have been made in
answer to this question but plenty have already been stated to get the four marks. The facts that are produced in the text will be more
than adequate for the needs of the examination. -CAD is used to design the item
-The software can be used to carry out tests on the finished design
-Completed designs sent electronically to CAM software
-which controls robot machinery to produce the item.
.
Notes: The difficult question first in this section. with no need to describe or explain.
(2)
A. the standard answers in the text. -This application may need more specialised routines than are available in off-the –
shelf software
-Many of the routines in the off-the-shelf software will not be relevant
Notes: A far simpler question than the first one. current packages
available would have been evaluated so there is probably some confidence in what
is available.
hence the relative costs of buying custom software compared to off-the-shelf
software would be very high as would the costs of the staff training. A question which starts with
‘Discuss’ is expecting a certain amount of analysis of the situation. The office manager would be keen to go ahead with the purchase as soon as
possible because all the decision making would have been done and the need has
already been established. though
notice that there is some relating to the scenario.
1.
Notes: Standard answers are all that will be expected from questions about the
standard software packages.

-CAD can be used to design the widget
-CAM can be used to produce prototype/help set up production line
-Spreadsheets can be used to keep track of the firm’s accounts
-Stock control software can be used to control the stock being stored in the
warehouse
-Order processing software can be used to keep track of new orders when they
arrive
-Payroll software can be used for paying the workforce
-Presentation software can be used by the salesman to impress the brewery firm.4. The important thing is not to be able to pick particular pieces of
software but to give a reasonable explanation of why that software would be used in
the given situation.
A firm produces widgets for sale to the brewing industry.
A brewing company may come to the firm with a proposal for a widget to fit a
particular container which will need to be produced by the firm which will then ship
the finished product in batches and invoice the brewing company.
. Sometimes the
sales team will be sent to try to persuade the brewing firm of the advantages of the
company’s widgets.
(6)
A.
Explain how the company can use commonly available software in the running of
its business.
Notes: It is possible to make almost any software fit the given scenario when it is
that wide in scope.

but is an attempt by the computer to understand human communication. a thermistor increases the voltage output as the temperature which it is
measuring increases.
Less obvious forms of automatic data collection are barcodes in a supermarket. These are seen on the back of credit cards and bank cards.
The most obvious type of automatic data collection is in a control system where the
computer collects its view of the outside world from sensors that give information about
the physical environment.) This signal must be changed into the stream of 0s and 1s that the
computer can recognise.8. this would not be suitable data input for a system which was controlling
the central heating in a house. which is rather
unreliable.1 Manual and Automatic methods of Data Entry
All computer systems need to have data input to them otherwise they have nothing to
process.
Automatic Data Collection. The code
is translated into a series of dark coloured bars on a light background so that the data can
be input to the machine without any further preparation. The data collection done by a sensor is continuous. often by sensors in remote locations. on which the data is stored
until a set of data has been collected and the data can be entered into the system in one
go.) The use of only some of the available
data is known as sampling. The methods of collecting the data can be divided into two types: automatic and
manual data collection. Analogue data is
physical data that creates a signal which consists of continuously changing voltage (for
example. and
by the use of magnetic stripes.8 Handling of Data in Information Systems
1. Many sensors that measure physical values are analogue
sensors while the data required by the processor needs to be digital.
Other forms of automatically entering data are by voice recognition.
Automatic data collection can be considered to be any data collection that does the two
stages of data collection and data input to the system without going through the
intermediate phase of data preparation to make it suitable for computer use. so that two marks side by side on the paper mean different
things because of where they are rather than what they look like. but a remote weather station on a mountain top where
different readings are taken every 10 minutes and then radioed back to the weather centre
once every 24 hours would need just such a device to store the data until it was required. and then stored until ready for
input to the system at a time that is convenient to the system. but perhaps every 5 minutes. Obviously.1.
The stripe contains information about the owner of the card in a form that the computer
. This is done by an analogue to digital converter.
A typical data logger will be in the form of a tape recorder. Another good
example is the school register which is taken by making marks on a sheet of paper and
that can then be read directly into the computer with no human intervention by an optical
mark reader (OMR). it is known as data logging. When data is
collected off line. This gives the previous
decision long enough to have had some effect. An OMR reads information by translating the position of the mark
on the paper into a meaning. but the
reading of the data is within a fixed time period (the processor does not want to know the
temperature in the room all the time.

this would count as automatic data collection
(it is known as optical character reading (OCR)).
Computer systems are available that will read individual characters and input them
without the data having to be transcribed.
Questions on this part of the syllabus will be suggesting suitable input methods for
particular situations. The
magnetic ink is particularly easy for the computer to read and contains enough
information to identify the bank and the account at that bank. All of this can be done with
no further human intervention after the original printing of the cheque book. which needs to be
input to the computer. Another form of data input used by banks is the magnetic ink characters
that are printed on the bottom of cheques before being sent to the account holder.
The most obvious is the form that has been designed to collect data.
Manual data entry. in other words the original data was not in a form acceptable to the computer.can use directly. An extra stage has been added here. the data has had to be
typed in.
the data that is written on the cheque by the customer (who it is made out to and for how
much) is not ready for input and hence requires some human intervention to make it
useable. An operator reads the data on the form and then types it into the
computer via a keyboard.
. and offering advantages and disadvantages for particular forms of
data input in different situations. However.

or a hand held scanner which can be rolled across the image a number of times
collecting a band each time. and the light intensity is measured of each pixel. witness the film
Forrest Gump.
Each of these image capture systems results in an electronic image being stored in the
computer system. The surface of the document is divided into small
rectangles.
the image is stored electronically enabling the user to download it into a computer and
manipulate the image and print out the images if desired. or pixels. It used to
be said that: “The camera never lies”. A
video capture card is an interface board which fits into one of the expansion slots in a
processor that allows the processor to store the values of the screen pixels for a specific
picture.
. it is then reported
to the computer as a bit map.
Digital camera.Methods of Image Capture
Scanner:
A scanner is a device that shines a strong light at a source document and then reads the
intensity of the reflected light. Image manipulation software can then be used to alter or edit the image
in any way that is required. Scanners can be of different sizes. Instead. In other words it allows the action to be frozen. these bands of image can then be matched up by the software
to produce the complete document.
Works in a similar way to an optical camera but does not store the image on film.
Video capture card.
A video picture is made up of a series of images which are changed approximately 26
times per second in order to fool the brain into thinking that the images are moving. While this allows the user to use their imagination and to tidy
up pictures or crop them to miss out unwanted parts of the image. this is certainly no longer true. typical is an A4 sized flat
bed scanner where the document is placed on a sheet of glass which is then scanned line
by line. it also allows
unscrupulous people to produce pictures with very little foundation in reality. A typical example of the use of a
video capture card is the market stall that uses a video camera to take an image of a
customer and then to select one image to print onto the T shirt.

8.
Validation. and will then be accepted as your date of birth despite the fact that
it is wrong. The third type of error is when something is typed in which simply is not sensible.
If the computer knows that there are only 12 months in a year then it will know that
181383 must be wrong because it is not sensible to be born in the thirteenth month. the use of parity bits to check data.6.
Checks on the sensibility of the data are called validation checks. The second type of
error is when the operator typing in the data hits the wrong key and types in 181193. it can be checked by the computer to make sure
that is a sensible date. It can be typed into the
computer with the utmost care as 181183. In this case an error has been made that should be able to be spotted if a
suitable check is made on the input.
Verification means checking the input data with the original data to make sure that there
have been no transcription errors. It won’t know which on is wrong but it can now ask the
operator to check that particular input. Parity bits and echoing back are techniques that are used to check that
data has been transmitted properly within a computer system (e. The first is that the data. quite
simply when you filled out the original form you made a mistake. This is
NOT validation. This type of data checking is called a verification
check. There is no reason for the computer to imagine that it may be wrong. There are three
types of error that can occur with the data on entry.2 Validation and Verification
When data is input to a computer system it is only valuable data if it is correct. In section 1.
.
Faulty data.g. or
the equivalent. The personal information kept on the school
administration system about you and your family may well be printed off at regular
intervals so that your parents can check to ensure that the stored information is still
correct. If the data
is in error in any way then no amount of care in the programming will make up for the
erroneous data and the results produced can be expected to be unreliable. is wrong.
Verification.f
checking of data was mentioned. The standard way to do this is to input the data twice to
the computer system. while
reasonable. The computer then checks the two sets of data (which should be the
same) and if there is a difference between the two sets of data the computer knows that
one of the inputs is wrong.
There is very little that can be done about faulty data except to let the owner of the data
check it visually on a regular basis. If the data does not
match up with the rules then there must be an error. If your birthday is written down on a data capture form as 18th of
November 1983.
The first thing is to dispel a common misinterpretation of validation. validation checks are used to check the input of data to the system in the
first place. There are many different types of
validation check that can be used to check input in different applications. it will (except in very rare cases) be wrong.1. Specifically. from the disk drive to
the processor).
Validation is a check on DATA INPUT to the system by comparing the data input with a
set of rules that the computer has been told the data must follow.

3.
2. it is at this point that the beeping sound would
normally be heard if everything is alright.
Each person has a unique national insurance number. As the stock file
contains details of all items held in stock. A particular application is set up to accept a national insurance number.
5. One number is special. A NI number has 9 characters. Existence check. therefore the code must have been wrongly read. A person’s name will consist of letters of the alphabet and sometimes
a hyphen or apostrophe. When the code is read at the check out till. it consists of
numbers. it is called the check digit. A mathematics exam is out of 100.
. Range check. A simple validation rule that the
computer can apply to any data that is input is that the mark must be between 0 and 100
inclusive. Check digit. it breaks the rule. if the arithmetic does not give the check
digit it must have been read wrongly. Consequently. if it is not there then the item cannot exist.
6.
which it obviously does.
4. 2 letters followed by 6 digits followed by a single letter. if more or fewer than 9 characters are
keyed in then the data cannot be accurate. The code is sent to
the main computer which will search for that code on the stock file. Character check. a mark of 101 would be rejected by this check as being outside
the acceptable range. When the code is read on the item at the supermarket.1. A bar code is read at a supermarket check out till. Length check. If the computer
knows this rule then it knows what the format of a NI number is and would reject
ABC12345Z because it is in the wrong format. This rule can be applied to input of a person’s name so that
dav2d will immediately be rejected as unacceptable. but they all have the same format of
characters. If the other numbers have
some arithmetic done to them using a simple algorithm the answer should be this special
digit. Format check.

3 Output Formats
When data has been processed by a computer system it is necessary to report the results
of the processing. visual. printout. Video is useful for demonstration of techniques where
there is little value in pages of instruction if a simple video can illustrate something
better. Sound can be
used for output from some systems. as opposed to the hard copy produced from a printer. Animation takes considerably less processing power than other
. If the system
allows the user to decide the type and range of output required during the run then there
is some positive user involvement leading to an interactive presentation where the user
can adjust the output to suit the example. This has the advantage of
producing the actual figures according to the values specified by the user.
Animations.
Graphs.8. and when two variables need to be compared.
Many applications do not lend themselves to a standard.
Video is a visually satisfying form of output that takes large amounts of memory to
produce because the nature of the medium requires large quantities of pictures to produce
the feel of continuous motion.
Reports
A report is a hard copy printout of the values of variables. a visual representation can
be very useful.
Graphs show trends very clearly.
Sound.
Images. indeed. However.
Interactive presentations.
Provide a good stimulus for an audience and lead from one slide to another when making
a slide based presentation.1.
‘Images’ can refer to any of the forms of output mentioned when they are shown on a
monitor screen. the specific values are not easily read from a
graph.
Video. obvious examples would be voice synthesis for
reporting to blind people and an alarm system to protect property against burglars.
The previous forms have relied on the format of the report being decided without the
luxury of being able to see what the figures look like in the first place. it is simply not possible to take reliable
readings to any degree of accuracy. the
figures themselves may need skill to interpret their significance and the value of figures
in a vacuum is often hard to justify. Different types of graph can illustrate different
characteristics. However the importance of the scales is paramount because otherwise a
very misleading picture can be given. Also. There are a number of different ways that the results can be reported to
the user. in a continuous distribution.

There are too many students for a one to one presentation all
the time so the college computer system has been loaded with demonstration software
showing an animation of the technique for artificial respiration. Doctors
come round the ward twice a day to check on the patients and make any adjustments to
their medication. This involves the nurse in using an
interactive presentation with the system. unless the image being animated is complex. Animation is used so often
that it can come across as being a boring technique that has just been added for ‘gloss’.
When considering output always consider the importance of timeliness and relevance. but is expected to
make the rounds of the patients to check on their progress at regular intervals. This may be accompanied by a
flashing light. this will involve the
nurse resetting values on the scales of the graphical output. needs to be taken. The nurse has other duties. if any. to quickly draw attention to the patient needing
attention. The doctor may well want to see a
printout of all the variable values for the last twenty four hours.
.
Output According to Target Audience
Imagine an intensive care ward at a hospital. or some other device. Some data is
not relevant to particular situations. the outputs are available for a variety of users. Once a week the nurse takes a first aid class at
the local sixth form college. a quick
glance at a screen showing a scrolling graph of the state of the patient’s vital signs over
the last 20 minutes will be perfectly adequate. If the graph looks in any way abnormal it
may be necessary to get a printout of the actual values of the variables for that patient to
determine what action. however up to date it is.forms of motion. There is
a nurse at a desk at one end of the ward. or even resetting the
parameters for setting off the audible alarm. which can be different for the same data in
different situations. although it may well be in other circumstances. When the nurse goes around the patients to make a visual check of their
conditions it is not necessary to know exact figures of heart rate or blood sugar. The colour of the patient’s
eyes has no bearing on their physical state and consequently should not be considered
relevant to this example. The data on heart rate from 3 hours ago is not going to be of
importance to the nurse looking after the patient. each with a patient who
is being monitored by a computer. but it may be of great value to the
doctor in providing a clue as to the reason for a sudden change in condition. The doctor may change the medication or the
parameters within which the patient can be considered to be stable.
If a patient is sensed by the computer system to have suffered a relapse while the nurse is
sitting at the desk.
Data tends to have a limited life span. There are six beds. some sort of alarm to bring the
notice of the nurse to the fact that something is wrong. particularly if there is
something happening to the patient which is difficult to understand. a sensible output would be sound. such historical data
can hold the clue to present symptoms.

finding faults in a car engine. etc.complex “thinking” tasks such as chess
.
If it is being used to diagnose faults.information gathered from experts is added to the knowledge base
. animals and chemical compounds (for example)
The Basic System
A basic expert system is made up of the following elements:
Setting up an Expert System
.the inference engine is created
. needs to be tested using data with known outcomes to see if it
functions correctly.g.tax and financial calculations
.the rule (base) is created
.the knowledge base is created
.prospecting for oil or minerals
.8.route scheduling for delivery vehicles
. For example:
.the user interface is designed/created (often use Yes/No options or multichoice)
The system. finding faults on a circuit board.
.diagnostics (e.information is gathered from experts in the field
. Usually a % probability of the accuracy of the
diagnosis will be given so the end user can decide whether or not to accept the
recommendations.identification of plants.1. once set up.4 Knowledge based systems
These systems have been developed to mimic the expertise and knowledge of an expert in
a particular field.)
.diagnosing a person’s illness
. the expert system will output the probable fault and
how to rectify/deal with the problem.

This gives
Expert Systems the ability to find solutions to diagnostic and prescriptive problems.lacks common sense in some of the decision making processes
. the response Why? came up since the user wanted to know the
Expert System’s thought processes. therefore potentially can save money
Disadvantages of expert systems
. To simulate human
processes it is necessary to have a vast amount of information stored in the knowledge
base and the reasoning set out as a set of rules in the rule base.never “forgets” to ask a question in determining the logic
.expensive system to set up in the first place
.reduces the time taken to solve a problem
.
In the above example.errors in the knowledge base can lead to incorrect decisions being made
.less skilled work force needed.provides consistent answers
. For
example:
If the make of car includes high performance and you want Italian style
Then the car you want is probably a Maserati Quattroporte
A rules base is made up of many such inference rules and the inference engine uses these
to draw its conclusions. It is possible
that saloon cars are a likely option. Up to now.cannot adapt to changing environments unless the knowledge base is continually
updated
. do you need a manual gearbox?
A: Why?
The system uses a rule base and an inference engine together to simulate human
reasoning when analysing a problem and arriving at a conclusion.
The above is how an Explanation System might work where questions like why or how
are dealt with. coupes are not likely.needs considerable training to ensure system used correctly by operators
.How does it work?
Consider this set of questions?
Q: Do you know which car you want?
A: No
Q: Is there any make of car you would prefer?
A: No
Q: Do you want 2 doors?
A: No
Q: Do you want high performance?
A: Yes
Q: When you have a big engine. I know that you like high performance which gives
me strong evidence that the car should include a manual gearbox”. The system would give the possible response “I am
trying to find the make of car you require.
Advantages of expert systems
. Inference Rules use an if-statement and a then-statement.

where the customer can have
their likeness printed on to the front of a sweatshirt. in other words any input device
may be alluded to in the question. in practice.
-and errors are reported to the operators.
-by the software.
-MICR
b)-Keying in can be used to place the details of the payee onto the cheque together
with the amount.
-MICR is already in machine readable form
-placed on cheques at time of printing the cheque book
-means that complex figures like account number do not have to be keyed in which
would invite human error.
-Camcorder where the image is sent to.
a) Explain how the data input would be verified. either to a disk for later entry. Describe two possible methods
of capturing the image to be printed. The syllabus actually says ‘including…’.
.Example Questions. as part of a fairground.
-a video capture card which produces a still image on a screen in the same way as a
digital camera does.
Notes: Although the answer is given as bullet points.
(2)
b) Explain why banks find the use of your two examples suitable for this application..
1. a)-Two operators would…
-independently key in the data
-The two copies of the data are then compared.
-in machine readable form. Note that although MICR is not stated in the syllabus. although.
(3)
b) Describe three different validation routines that could be performed on the data. the devices used in the
exam will be common and relevant to a simple situation. These are
keyed into the computer system by operators.
2.
A mail order firm receives orders from customers on paper order forms.
-or to store the data on a disk for future use.
(4)
A. the
examiner expects you to have a working knowledge of it and other input types not
stated. a)-Keying in of data..
b)-Article number can have a length check carried out on it.
3. the name of the customer and the date that the
order has been received.
A small stall is to be opened. (6)
A. -Digital camera
-connected to the computer which uses
-software to crop and present the image to the printer. or directly onto the cheque in
machine readable form. the response expected would
be a prose explanation. The data that is to be keyed in
includes the 5 digit article number... a) State two methods of data entry used by banks in their cheque system.
(4)
A.

. the report gives precise figures.
-to show the operator the trends in the vessel.
.
(2)
A. along with many others.
it is reasonable to expect students to realise that heat.
Explain what is meant by the timeliness and relevance of data.) showing the general state of the reaction
vessel.
4. Having said that the answers here would
not be expected. would play an important part in the reaction.
-while the graph shows a trend.
-Report (of temperature). meaning that the examiner wants to
know what the type of check is.
-to allow investigators to study problems that may cause a shutdown or
unacceptably poor product.
Notes: Do not use the verification technique of printing out the data so that the
customer can check it. There are many possible alternatives for part (b).
-Relevance of data means that data has a bearing.
Note: While knowledge of a chemical reaction is not part of a computing syllabus.-if there are not 5 characters then the article number must be wrong. -Timeliness is the concept that data changes over time and that data is only part of a
sensible solution for a short period before it becomes outdated.
Notice that there are two answers for each one. Describe three
different types of output that would be used by such a system. Choose them carefully
so that there are three different ones and so that all three pieces of data are used.
-Sound
-an alarm would sound if the temperature went past a safe limit.
-The date can be subject to a range check (actually a number of range checks). for example shows clearly whether
the temperature is increasing..
-any characters other than letters or hyphen or apostrophe must mean that the check
has been failed. in that particular
application.
-the first two characters must be less than 32. -Graphs (of the temperature.. and also the rule that has to be followed by the data
to be treated as valid. stating why such a
use would be necessary.. or some other sensible
parameter.. Examiners are aware that students take these papers under a lot of
pressure and in a question like this will do their best to compensate as long as the
germ of the answer is there.
-Hard copy printout.
(6)
A. pressure.
-Name of customer can be checked with a character check.
A reaction vessel in a chemical plant is monitored.
Note: These are simple definition answers.
5. or use. This is a mail order company and hence this would be
impossible. by a
computer system using a number of sensors of different types. any answer that has the essence of the correct answer would be
acceptable..

In the last chapter mention was made of the nurse looking
after a group of patients. allow the user to input all the data that the user thinks important.9 Designing the User Interface
Importance of Good Interface Design
However complex the software. The interface design for a
pre school playgroup to learn about numbers is going to be very different from the design
of an interface for the manager of a chemical plant to keep a check on the reactions
around the plant. The HCI
must be unambiguous. The circumstances under which the interface is to
operate are also important. The interface that this manager would use to study a particular reaction
(perhaps tables of figures. or graphs showing the different parameters of the reaction) is
very different from the interface the same person would use if they were wanting to see
the flow of a chemical around the whole site. In those circumstances an audible warning that a problem may
be occurring is far more sensible than a visual one which may be ignored if the nurse’s
attention is drawn away from the screen. the
system is unusable if there is no intuitively simple to use interface with the human being
who is in control of the system or for whom the system is producing results. This would probably be in the form of a
diagrammatic representation of the site.
. however expensive and powerful the hardware.
The intended user of the interface must be taken into account. If
the user is using the computer to play a game then the paramount importance of the
interface is that it adds to the enjoyment of the user.
 who it is for
 what information needs to be conveyed
 the circumstances under which the interface must operate
 the effectiveness of the communication
 the enjoyment obtained from using it
are all important when the interface is being designed. namely the transfer of
data into the system and the communication of information from the system to the user.
and produce the output in an easily understandable form.1.
Consideration of the purpose of the interface. Finally. the designer of the interface needs to
take account of the purpose for which the interface was designed.

Colour is an important part of any HCI.
The content of the information presented is important because a user will soon begin to
ignore items of information that are constantly being put on the screen despite not being
necessary. perhaps in the form of a
scrolling graph. Such data is very transitory in nature because the screen display is being
constantly updated. The different levels of contrast between colours are necessary if the individual
items of information are to stand out.
Colour. if a method is used to show that a piece of information needs urgent
attention.
Visual perception.
Layout. If the information
should be seen in an order. or can be used to distinguish one type of information from
another.
The layout of the data on the screen is important.
This includes all the information that is presented by the system in such a way that it can
be seen with the eyes. This means that the information will be presented on a screen or on
a hardcopy produced by a printer. The eye naturally reads from left to
right and from top to bottom.HCI Design Issues
Short term and Long term memory. Some of the
information is presented via the user computer interface.
The information produced by a system can be of such a large volume that it is not
possible for all the information to be stored for future use by the user.
Content. Such data is part of the short term memory. as the eye naturally reads. The long term memory is
that which stores the data for future reference. This means that more important information should be
positioned toward the top and left of the screen. then the correct screen order is from top left to bottom right
corners. Similarly. The contrasting use of colours can highlight the
more important information.
. The size of individual pieces of information will be
important as will the contrast used and the type of font in the case of text. then all such highlighted
information may be begun to be ignored in the same way. while dark blue on black is very difficult to decipher. Black on white provides the highest possible
contrast. The volume of information on the screen
at any one time is also important because there is a limit to the amount that the eye can
follow and the brain distinguish in one sweep of the screen content. while the operator does not perceive the urgency.

-Hard drive for storage because.g... Each answer needs to be expanded a bit because of the word
‘describe’ in the question.
Notes: The standard form of the hardware question requiring answers for
input/output/storage/ and communication where appropriate.
Communication:
-Necessary for communication.
2. Some work in the office using the
computer system for administrative tasks. the answer
must be limited to software because of the question. Office:
-Keyboard/mouse for input because…
-input is likely to be character based owing to typical office tasks.
-Monitor/laser printer for output because..
-The hardware that is going to be used to communicate in the HCI.
Describe the factors that would have been important in the design of the software
interfaces to be used by the office workers and the shop floor workers.
(6)
A. -Ability of workers with computer systems..
(12)
A.
-will determine style of interface.
-produce design quality drawings for use in manufacturing process.
-Hard drive for storage in order to.
-Plotter for output in order to.
-of need to store and retrieve documents out of sequence. giving
reasons for your choices.
-The office will probably use text while the..
-store number of high quality drawings.
-output needs to be checked and then high quality printout for documents to be sent
outside firm. either between machines or to some central
resource/LAN.
-requiring cabling/network cards.
-colours will have to be different on the screen in order to maintain contrast..Example Questions
A company has a workforce of around 2000.. touch screen input or keyboard.
-shop floor will probably need diagrammatic responses.
-have they received training/are they used to computer use…
-The environment in which the system would be used…
-lighting conditions on the shop floor may be different to those in the office. These are standard answers
taken from the text. while others use the computer system on
the production line for giving details of orders that need to be manufactured.
Select appropriate peripheral hardware for these two application areas... e. In reality this is too
.
Factory:
-Touch screen for input because..
-dirty environment could damage other forms of input device.
1.
-What output will be expected from the computer?..
Notes: Although the hardware has been mentioned briefly in passing.

-or to miss any out.
3.
-Sound so that.
-produced by a plotter.11.. but the important point is to test whether the student understands the
concept of a form based interface.
-Validation routines will be set up on each data area.
Passive information systems are systems that will answer queries based on the data that is
held within them.
Chapter 1.big a question to be asked in an examination. but the data is not altered.
(4)
A.a Passive and Interactive Information Systems
An information system is a system that provides information according to a user’s
requests.4. -The interface will have specific areas to hold the answers to questions.
-Hardcopy printout of the plans for products. There is an element of testing the candidate’s ability to analyse a
situation here.. standard answers which will gain full marks even if many of the
points are missing.
The office workers often have to key in the details of new members of the
workforce.....
4. the normal question will be out of
3.
-an alarm can be sounded if the line is travelling at the wrong speed.
-so that they can be taken from the terminal and used at the point of manufacture.
-to check the data entry and reject anything not sensible.
-making it difficult to put the details in the wrong place.
Explain the types of output that would be expected from the computer on the
factory production line. -Menu type of interface on the screen so that…
-a touch sensitive screen can be used for input. The details of the worker are on a standard form which the new
employee fills in. if it is used to control the speed of the production line as
well as being used as a tool for the workers.
Passive information systems.6 or 8 dependent upon whether the question says state or describe and whether
communications play a sensible part in the application.
-these should match the positions of the answers on the paper form.
(4)
A. Explain how a form based software interface would be useful to
the worker who has to key in the data..11 Characteristics of Information Systems
1.. A simple example would be an electronic
.
Notes: Again.
-Some areas will not allow a non reply.

or to look up their telephone
number in order to contact the parents. but also
updates the number in stock immediately (interactive) so that when the next item is sold
the number in stock has already been altered.
An interactive system is one that data can be entered for processing which may alter the
contents of the database.
Interactive information systems. An example would be the school secretary updating the
attendance record of a pupil in the pupil file. Another example
would be the student file in a school that can be accessed by members of the teaching
staff to find out where a student is at a particular time of day.encyclopaedia where queries can be used to search for data and much valuable
information can be learned. In commerce. The database of information is a valuable resource
but it is not possible for an ordinary teacher to alter it. but the user is not allowed to alter the data.
. a stock control system in a
supermarket is an interactive information system because it not only gives information
like the price and the description of the goods for the till receipt (passive).

One is the day to day management of the organisation.1.
.b Management Information Systems
A management information system is software that allows the managers within a
company to access and analyse data. what new items to stock. making decisions about
what items of stock to keep.
The second of these management tasks is to look at the wider picture. is usually working on two
levels. which workers are
having to do a lot of overtime which may point to the need to increase staff in that sector. what to discontinue…
The first of these management tasks is condition driven.
keeping track of invoices. which areas of the business are doing well and which are not.11. The information system can be
used to trigger decisions that have to be made. These levels may be different levels of management or may be the same people
but with two different tasks. A certain item is reported to be low in
stock by the system requiring a decision to be made as to whether to reorder and how
many to reorder. or any other organisation. ensuring that the business has enough stock. arranging for the
workers to be paid… The other is the strategic management.
The management within a company.
Such reports are termed Strategic level reports because they inform the executives who
need to decide the strategy that the company is to follow. To extract
information from the system which can inform wider decisions like should an item be
stocked.

1. an examination question will expect the student to be able to decide
which of these two types of processing are most appropriate in a given situation.
that processing will tend to be of the same type for each set of data and that human
intervention is not necessary. It is not
sensible to list a number of different applications for each type and to expect students to
learn them.
This work has been covered in module 1. The application in a question may not be on the list and the student would not
be demonstrating an understanding of the concepts even if it was. The other example is in information systems where it becomes necessary
to update the file of information before the next enquiry is dealt with. A good example would be the control of a robotic machine on the
production line. otherwise the second person may be sold the same seat. If a customer enquires whether there is
a seat available on the flight.
In general terms. the mail
order company will need to change the number of items in stock before the next query
arrives.
then the number of tickets now available must be updated before the next person makes
an enquiry.
Rapid response processing.
. The classic
example is the airline (or theatre) booking system.
A batch processing system is used when the output does not have to be produced
immediately. Real time processing can be
thought of as being used in process control where the results of the process are used to
inform the next input. Far more sensible is to
learn to recognise the characteristics of each of the types of processing in a given
application.11. In module 1 we saw that the perfect example of batch
processing is the payroll system. and in response to a positive reply decides to buy the ticket. Similarly.c Applications requiring Batch Processing/Rapid Response
Batch processing. and nothing has changed because we are in a different
module. Other factors are that the application will tend to use a large amount of data.
In module 1 this was referred to as real time processing.

(4)
A.
2. a) -Batch processing is the processing of data by collecting the data and then
processing it in a single batch.
A company payroll system uses a personnel file among others.g.
Notes: The amount of material that is covered in this section is so small that there
are very few questions that can be asked.
Notes: The use of different operating systems at different times to perform tasks
within the same application area provides a very popular question.
.
-Enquiries by employees need to be handled on a one off basis. giving an example of each. consequently perfect for batch processing. A system that controls the progress of a computer controlled robot vehicle
around a factory.
b) -Payroll needs to be run once per week and. (4)
A.
a) Explain the difference between batch processing and rapid response processing.
-e.
Explain the difference between a passive information system and an interactive
information system. (2)
b) Explain how batch processing and rapid response processing can both be sensibly
used in the context of the personnel file being used to calculate the payroll.Example Questions
1.
-Rapid response processing is processing where the result of the processing is
needed immediately..g.
-requires no human intervention.
-with the result of the enquiry being made available to the employee immediately. This book when it is installed on a network
-An interactive system is one where it is normal for data that is either offered to it or
which it produces will also have the effect of altering the data stored. in fact this just about covers all that can be
expected of a candidate. -A passive system is one where the database is not changed
-e..

In the 1980s IBM. and to
larger businesses where information systems were needed to produce payrolls and other
information hungry examples. but there was undoubtedly
an element of such workers protecting their position by making computer use seem
somewhat mystical.12 Implications of Computer Use. Gradually. It certainly helped that
Microsoft operating systems were installed in the cloned machines. The results of this are still seen today in the attitudes of many middle
aged and older people who believe that using a computer is beyond them. Until
these machines no one thought that ordinary people would want a computer. manufacturers decided to copy the way that it was built. in Britain. as the IBM clones grabbed a larger and
larger share of the market. small. useful. although Acorn. it had 1/4K memory! But it did
mean that ordinary people could own their own computer.
Such a seemingly mundane argument over something that only carried prestige for the
eventual winner of the argument. There was some justification for
this in order to use a scarce resource as effectively as possible.
This mentality gave rise to the concept of ‘Fortress Computing’ where computer
competent people kept others away from the systems. relatively easy to use machine called the Sinclair
ZX79. for instance.
1. but because it meant that these machines could
. the world’s biggest computer
manufacturer. It was not successful. stored program machine is now acknowledged to have been the
Colossus which was a computer that was designed to break the German Enigma codes
during the war. decided that they would produce a small machine. but something with which they were brain washed when they were younger. so parents wanted to buy one for their children to
use in order to help with school work.12. Confusion over which computer was the first has been rife because of
contrary claims and a lack of definition of what constitutes a computer.
but many other. Different centres
around the world fiercely put forward their claims to have invented the first computer. was a symptom of the jealous way
that people who were involved with computers and who were able to use them guarded
their privileges from others. not money or power. There was very little it could do. There was
no real market leader. and there was a plethora of machines.
The use of computers was largely confined to this technical elite in universities. were very popular because their
machines were being used in schools. the phenomenal success
of the ZX79. The revolution in computer use came in the late 1970s
with the invention of a cheap.
Each machine needed its own software and many started to go out of business. ZX80. This is not their
fault. and then the Sinclair Spectrum proved that there was a market.Chapter 1. the other companies went to the wall.
The first effective. suddenly
many manufacturers jumped on the band wagon. Such
machines were called IBM clones.a Changing Trends in Computer Use
The history of the computer has been remarkably short for a device that now pervades
every aspect of our society and effects the lives of so many people in a serious way. Also. an
argument that was settled by the lifting of the official secrets act from Colossus in the
1970s. not because they
were the best operating systems. smaller.

and the effects are what are discussed in
this chapter. will have a wider variety
of choice from the supermarket than they could get locally. not based on accident of birth.
Note that many of the changes made to our life styles have been forced rather than being
made by choice. if they want to book a holiday there is a 40 mile
round trip to find a travel agent in the nearest town.
When we add to this the fact that one of these people used to be employed by the bank to
run the branch in the village. order goods from the supermarket
20 miles away at a lower cost than buying them from the grocer. The second person does not have a computer. there are still
large numbers of the population.
The effect of this has been enormous on society.communicate easily and that files were compatible.
Imagine two people who live in a village. has to use the village shop with much higher prices. These two people are very different
in their life styles and the social changes that have occurred to.
but based on whether a person has access to the information revolution. not just one of them. while the other has been told to go
on a training course to learn a new piece of software.
. that do not have
access on a regular basis. They will be able to book rail
tickets. the scale of how much our lives are
being effected by the use of new technology becomes even more evident.
The last bank in the village has closed because it was too costly for the bank to maintain
the branch which was losing money because so many of the villagers had changed to
running their account on the Internet. even in a rich country like Britain. Nowadays.
because of the computer are immense. through the Internet. there is a higher number of computers in homes than there are refrigerators
or baths. The village has a grocer’s shop and newsagent. There is a distinct danger that this will lead to another form of
class-divided society. which will also allow them to pick up holiday
bargains. A person living in this village that has a computer
connected to the Internet will be able to pay their bills. and does not have the
convenience of ordering on the Internet. so has difficulty with having a
bank account. at a discount. However. and increasing daily. or based on wealth (or lack of it).
world wide. but is now out of work. we have a society where.
25 years ago the proportion of the world’s population that had access to a computer
system was tiny. nowadays it is very high.

Although this may be seen by
some as being an uninviting prospect. This change in working practices is another example of the technology
creating two classes of people (Section 1. particularly boys.
Work practices are changing in a number of ways. This means that people can work from home for at least
part of their week. those able to learn additional skills
and those not.
 Computers have meant that some repetitive tasks have been taken away from human
beings.b Changes in Leisure and Work
Computer availability and acceptance has brought about large changes. Many
jobs have been lost to the human work force in this way.1.12. Less positive is
the ability of the electronic systems to report the working practices of the workers to
their boss. and also leads to
expansion and the creation of additional jobs. companies that
have invested in this way have tended to become more profitable which has the effect
of safeguarding the jobs that are still offered by the company. it does not need paying.
someone has to build the robot.12. many years before their parents
generation would have shown such symptoms. A robot on a car production line can not only work more consistently than its
human counterparts and do the jobs of many people. but also in the way we use our leisure time and in work practices.a). someone has to write the software to control it. Although
there is no hard evidence of a link between playing such games and anti social behaviour
of the child themselves. not just in the
ways that we live. This type of work practice is becoming less
.
 The use of technology allows people whose jobs require a desk and who can
communicate satisfactorily with their colleagues without needing to be in the same
physical environment to have their desks where ever they want by using electronic
means of communicating.
someone has to maintain it. Every time a robot is placed on a production line. This is a very insular way of passing the time which
is beginning to worry educational psychologists because children who behave like this
are in danger of not forming the social bonds and learning about the social interaction
necessary in later life. Long hours
spent in front of the monitor screen at an early age is becoming suspect in the amount of
RSI and other injuries being suffered by young adults. Some of the games are particularly violent. there is a growing belief that there is such a link. The problem is that the majority of jobs created require
more skills than the jobs that have been lost. The implications are far reaching. This in turn means a ‘skilling up’ of the
workforce. Less pollution because of fewer
commuters and pleasant working conditions are both positive factors. and the lack of social contact which is so important in maintaining job
satisfaction.
Children. or anti social.
 Additional jobs are created. spend long hours of their leisure time in front of computer
terminals playing computer games.
 In the past it would have been quite normal for a person to start a job after leaving full
time education and to stay in that job until they retired. However. it does provide for security and gives automatic
prestige to even the most lowly of workers because of their seniority within the
business bringing invaluable experience.

Nowadays. As a stock holder it is possible to buy and sell stock at any time of the
day or night simply by using one of the markets open at the time. the
performance of which might effect others when they opened. each country had its own stock market. Twenty years ago. and the worker is never far from being contacted
and consequently can be at work at all hours of the day.
Communication can be immediate. no longer is it
necessary to wait for the national market to open the following day.
Electronic communications have changed the way that business is done. the stock markets of the world are all
interconnected.
.
and less common as modern technology changes products. manufacturing techniques
and the life cycle of businesses. A good example is the
world’s stock markets. but they tended to be
fairly insular in their dealings.

An interesting experiment is to change your initials every time you
have to give your name. A
typical effect of this passing on of personal information is the junk mail that comes
through the letter box. Consequently it has become important to
protect individuals from misuse of their information by legislation and by measures that
restrict both the access to the data and the passing on of the data to other users.
There would be no problem if it could be ensured that all the users of the information
were going to use it for the right reasons and that the information was always accurate. Distance is no object either. Within a relatively short space of time junk mail will begin to
arrive and by reference to the initials it is possible to work out who has sold your details
on and to whom they have been sold.
.
Unfortunately the use of electronic information does not recognise national boundaries
and some authorities are not as anxious to uphold the rights of the individual as others.c Privacy and Confidentiality of Data
The expansion of computer systems around the world have given rise to more
information being stored about individuals than ever before.
however these things cannot be guaranteed. The problem is that to get
another copy of a person’s information the only thing that needs to be done is to press a
button. Using electronic communications it is possible to
send a person’s information from one side of the world to another in milliseconds and
then to store that information in a system that the owner of the information is unaware of.12.1.

in other words was stored on a tape or a disk. Each country will pass laws that are particular to that country. exemptions for reasons of national security or because it is thought
to be in the individual’s interest. on request.
 not be kept longer than is necessary.
Attempts have been made to harmonise legislation across boundaries. but it is difficult to get agreement when
individual parliaments still have sovereignty. in the case of a computer system it would
protect the person who has written the software rather than the user or the person whose
details are being stored. This shows that.1.
Any personal data that is stored in a computer system must
 be accurate and up to date.
but they largely follow the same model that is used in Britain. This has now been changed by the
latest version of the act. Access to the data must be strictly controlled. just like everything else in the world of
computers.
 be available.12. It did not apply to data
stored on a CDROM because that is stored optically.
Other measures that could be expected would be some control over the passing on of data
to other organisations.
In Britain the Data Protection Act that was passed in 1984 only applied to data that was
read magnetically.
. to the subject of the stored data.c.
Copyright law protects intellectual property. The European
Union pass their own directives about data. The purpose of such legislation is to protect citizens
from something that by its very nature can be insidious because it is difficult to
understand the consequences of unrestricted use of personal information.12.
 be relevant to the task for which it is intended to be used and used for that original
purpose.
Legislation protecting personal information must not be confused with copyright law.d Legislation
Most countries have now enacted legislation in attempts to overcome the problems that
were mentioned in section 1. things change very quickly and that human systems often find difficulty in
keeping up with the changes.
 be kept securely.

there is no one in charge. the obvious example is
paedophiles using the net for their own purposes. There simply is no ‘They’. There can be as many
telephones as you like. they are legal in Holland. “They should have that page removed.” They are showing their
lack of understanding of the net. If the control of the
net was in Britain then the law would say that these things would not be allowed whereas
if it were in Holland they would be allowed.e Controversial Information
The Internet was originally started by the American military (ARPANET) as a means of
communication in time of war.1.
There are some things that all sane people would condemn. The truth is that even if the Governments of the world did not want the
net there is nothing they can do about it because how can they pull the plug on millions of
machines all at the same time?
. The principle was that if a communications system has a
central control system (like a telephone exchange) then it is easy to disable that
communications network by destroying the central control. When someone complains
about the fact that there is a page on the Internet that shows anyone how to make a bomb
and says something like. But do
our values necessarily apply in a different society? Do we have the right to subvert
another society by using the net for propaganda purposes? If we do then why should we
get upset when values that are not to our liking are sent back to us?
If the world wants an Internet then it will have to put up with the downside of an
uncontrolled information network as well as the advantages from instant mass
communication.
This is the whole principle of the Internet. without an exchange they are useless. if there were some central
body set up to control the net and to make sure there was no paedophilia on the system. however. We would contend that the Internet is a
useful tool in the fight against oppression and the suppression of human rights.
where would the line be drawn. ARPANET was devised so
that there was no central control and consequently the losing of one part of the system
does not stop the rest of the system from operating. there is no control. However.12. Hard core pornography and the use of cannabis are
against the law in many countries.

The simple cure for this is to take regular
short breaks and to move around and exercise the joints and muscles.
Despite the problems that are associated with the computer itself. While these worries have
probably been exaggerated in the past.12. Over time. We are not designed to sit for long periods of time.
Much has been made in the past of the radiation that comes off the screen. and the more modern screens are far safer anyway.
as can the use of anti glare screens fitted to monitors to cut down the levels of contrast so
that the eye can handle it better. the arms to carry things and support weights.
Eyes did not evolve to stare at a flat surface that is very close for long periods of time. A new condition has been
identified called repetitive strain injury (RSI). This produces tears which
lubricate the eyeball. where a new network has been
bought with little thought for the classroom that it is going to be squeezed into. supporting the
weight of our own arms while small movements are made by the hands to press keys and
our wonderful 3 dimensional sight is used to stare at a flat screen no more than a metre
away. and the
possible damage that can be done because of the radiation. The use of glasses to help the eye to remain
focussed and regularly looking away from the screen can help to alleviate these problems.
The result is that cables are left trailing and that the furniture used is not always suitable. as with any misuse of the body the long term use
of computer systems in this way will cause damage. Too much enforced staring at one point can lead to a condition
called dry eye which can be very painful. naturally. Are there
enough plug sockets or are too many pieces of electrical equipment going to be run from
too few sockets? Can the cabling be put in trunking? Is there adequate ventilation and is
.1.
Many schools provide good (or bad) examples of this. Joints in the fingers and the elbow and shoulder are
made to perform movements that they normally would not do. the eyes are designed for 3
dimensional vision.
The human body is very resilient. the most important
problems are less to do with the machines themselves. move about in the socket. these strains on the body can lead to pain
and to restrictions on movement which are difficult to ignore. and to perform them
regularly over long time periods.
there is a lesson to be learned from the research into radiation from mobile phones that
demonstrates how even small amounts of radiation can be harmful.
Muscles that are not designed to support relatively small weights (the arms) for long
periods of time when using the computer keyboard begin to be strained. Also helpful is the
use of a Natural Keyboard which allows the user to sit naturally while working.
The eyeball should. The eye can also tire because it is being made
to use a fixed focus for long periods. The human body is not designed for long
periods of inactivity.
Many computer installations are housed in rooms that were not designed for such use. particularly when
such small movements are made. but.f Health and Safety Implications
The human being is not a sedentary animal. The legs are designed to move us
around. The body is designed to move.

12. This can lead to feelings of
inferiority and stress on the older workers.b it was mentioned that the new technology allows remote working in
many situations. If the chairs are not comfortable then back
problems can occur.
In section 1.
Working with computers can cause stress.the lighting suitable? If the lighting is the ordinary classroom lighting then it will make
the screens even more prone to glare. This situation has changed for many people because of
the use of computer technology. While there are substantial benefits accruing from this practice there are
also problems brought about by the lack of social interaction that human beings get from
a shared work environment. These can be lessened by using ergonomically designed seating
which encourages good posture.
. Historically. particularly among workers who were not
originally trained to use them. Because of the need to keep up to date with the latest
hardware and software it is now the young people coming into the firm that are more
experienced than those who have been there some time. once a worker has attained middle age they
should be more experienced than the younger people coming in to the firm who will
probably be working under them.

The explanation is
simple. When you send something for printing. and some parts of the chassis can be
melted down and reused.
When computers are eventually finished with and need to be replaced. This has obvious advantages in that the
pollution is cut down because there are fewer vehicles on the road. however an understanding of the implications of
the use of computers would be incomplete without comment about our environment. with an
electronic office this was no longer necessary. There is an environmental cost
here on two fronts.Environmental Issues
Strictly. In the 1950s LEO was invented. However. With the
introduction of machines the amount of paper increased massively.
Many years ago the use of computer systems in the office was hailed as the start of the
paperless revolution. The environmental implications of this
were tremendous. There is a minimal saving at the office block because some workers have to go in
to work and therefore the office block must be fully heated. there is an element of people being able to
work from home rather than having to commute.
The computer systems themselves have to be produced. much of the content of a system is not economically
viable to reuse and consequently is discarded. but ‘how many do you use?’ The
difference is that if you have made a mistake you correct it and get another printout. no more burning of the
documents that are no longer needed so that they remained confidential.
how often does the printer produce an extra sheet? Do you save it and put it back in the
paper tray? How often does the printer not print properly making another printout
necessary? How many people printing off a spreadsheet haven’t given the limits of the
sheet so that the printer has printed 20 or 30 sheets of blank cells before anyone has
noticed? The same sort of things happen in business. the computer requires a certain amount of power to enable the factory
to make it. and then there are the raw materials that are needed in the manufacture. ‘how many do you hand in?’. When it is also realised that
some of the contents of a system are heavy metals and other toxic materials the
environmental problems of replacing a system are great. if
you were using a typewriter you wouldn’t do that. How many sheets
of paper do you use? Not. As the life of a system in business is about
two years this adds up to an enormous waste of resources. this is not part of the syllabus. Some is recyclable. Consider a project that you are doing for one of your courses. Chips are heated in
order to recover the gold used in their manufacture. It was the Lyons (same company as
the cakes!) Electronic Office. The idea was that paper would “become a thing of the past”
because messages would all be sent electronically. There was one tiny problem. because if 50 people don’t go in to the office it is an additional 50 homes (offices
in those homes) that have to be heated that day which would not otherwise need to be
heated. No more cutting down forests to provide paper. there is a large
amount of hardware that needs to be got rid of. but it is not all good
news.
. so what should have been good
news environmentally has tended to backfire.
As has been mentioned before in this chapter.

-Parents may use the computer to work from home…
-cuts down the time spent commuting to work and allows for more leisure time…
-but may increase stress and worry about work because of reduced contact with
colleagues. so don’t start to talk
about workers losing their jobs.
(4)
A.
Discuss the implications for customers of a travel agent closing down their agencies
and doing all their business on the Internet. the question does use the
keyword ‘discuss’. stop.
3.
(2)
Data can be misused…
-by insurance companies to alter an insurance premium. so don’t just write notes.
-Customers with disabilities. -Lower overheads for the business…
-meaning that customers can expect to pay lower prices. If
you were thinking of saying that they could send emails rather than write letters it
may be worth a mark but is a little trivial for both marks.
-by thieves who want to know which addresses have large premiums and are hence
worth burgling
-by employers who can check on employees moonlighting. This would be a nice starter
question for a paper.. if things go wrong.
Notes: Sensible to use obviously different members of the family. many different possible answers. but…
-effects their social development.
Although the mark scheme would be set out in this way.
-but customer may find more difficulty in finding the information required because
there is no assistant to help. It may be true. particularly blindness may be more disadvantaged
than most
-Complaints. so don’t waste too much
time.
Notes: Again.
Describe two ways in which a computer system in the home can alter the
interaction of the family with the outside world. Need to say at
least two things for each one because the question uses the keyword ‘describe’.
. the examiner is looking for a coherent
argument which contains six of the sensible points.
(6)
A.
-Customers who have the Internet will be able to access late bargains
-Customers without the Internet may find difficulty in booking any holiday. -Children play computer games…
-stops them going out and consequently they are safer. The question is quite
specific about it being from the point of view of the customer. as it expects simple one line answers.
State two reasons why it is necessary to protect the confidentiality of information
stored about people.Example Questions
1. but does not answer the question. When you think you have earned the marks.
Notes: There are other points to make but only 6 marks.
2.
-Information will always be up to date because up dated centrally. will be harder to make.

5. -There is a danger that those pupils who have access to the Internet outside school
will use it anyway.
(4)
A. Any three of the measures listed in section 1. leading to many copies being produced.12.
7.
(6)
A.
6. and…
-therefore it is only right to allow access in school. They contain toxic material which can harm the
environment. It is such an important area of the syllabus it is
likely to be asked on a regular basis.
.d. -The use of large amounts of paper because…
-everyone now expects that when a final copy of a document is produced it is
perfect.
-Eye problems caused by staring at the screen…
-Wear glasses and fit anti glare screens. -RSI…
-Use sensible keyboards and properly designed furniture to encourage good posture.
-Problems associated with radiation from the monitor…
-Sit further away from the monitor screen.
Notes: This is a banker question.
Describe two ways in which the use of computer systems in business has harmed
the environment.4.
Outline the health problems that may be experienced by telecall operators and state
how such problems could be overcome.
Describe three measures that would be expected in a country’s data protection
legislation. the problem for the examiner is that there are
only a few ways of asking the question.
-The high turn over of machines means that many new machines have to be
produced and…
-the old ones must be disposed of.
-Pupils may find inappropriate sites…
-which means that the teacher has to censor the material in some way.
(6)
A.
Describe the consequences of allowing upper school pupils to use the Internet to
find information for project work.
(4)
A. Candidates should learn the measures stated
in the syllabus and use them to answer the question.

The sequence of steps that need to be carried out in order to solve a problem. In this case the algorithm
is
1. In maths we use formulae for showing the solutions to simple problems.
Multiply the result by 2
4.
1. While it is a perfectly good description of the
algorithm here.
Consider the problem: How to calculate the perimeter of a rectangle when it has length (l)
and breadth (b).
Find the length and breadth
2.
2.
Consider some other methods for writing down an algorithm.2 Practical Programming Tools and Techniques.
Add the length and the breadth together
3. There are two things that have to be done to produce an algorithm to solve this
problem. We have to times by two. We all know that the answer is obtained by simply finding the lengths of
the four sides and adding them up. Either of these formulae will
work. Indeed. This is a prose solution to the problem because the answer
is given as though it is spoken language. and when we are considering an algorithm some may be more efficient than others.
End
3. Another way of showing this order is to use arrows pointing from one instruction to the
next
. is called an algorithm. The difficulty with spoken language is
that it is hard to describe more complex solutions because of ambiguities. the
answer should be worked out. they must be done in the right order or the answer
will be wrong.1 Designing solutions to problems
Structure
The solving of problems using computing techniques relies heavily on being able to
divide the problem into a series of steps that should be solved in a sequence in order to
solve the entire problem.
2. and we have to add the length and breadth together.
However there is one further factor. This leads to another way of writing down an algorithm: write down the
steps and number them so that they are done in numerical order. which takes
into account the order of the steps.
There are a number of ways of presenting such algorithms.
but if they work out the answer to the problem then that’s enough. the last sentence is an algorithm. the problem is a very simple one. in this case
Perimeter = length + breadth + length + breadth
or
Perimeter = 2 * (length + breadth)
It is important to realise that there is no single right answer. It tells you
how to solve the problem that has been set and if the instructions are followed. A simple algorithm
like this can sometimes be expressed as a single formula.

Find the length and
the breadth
Add the length and
the breadth together
Multiply the result
by two
End
The example shows the individual instructions in nice neat little boxes.
. this is certainly
not necessary. However. This type
of representation of the algorithm is known as a flow diagram. and also uses the normal rule of reading down a page. providing
the arrows are in the correct order then the instructions can be placed anywhere. some of which you will
meet later in this course.
There are many other ways of defining the solutions to problems.

and correct them. the problem to be solved is likely to be
far more complex than the calculation of the perimeter of a rectangle. the lights and other output devices being controlled
are the same.
 Last month. Collections of modules like this are known as
software libraries. This means that the finished software should be more
reliable when it is being used. so our company uses Aisha to solve the
problem of collecting the information from the sensors. and the number of roads is different so Leon will still need to come up with a
solution for his module. consequently the problem should be solved more quickly. in that we started
with an original problem (the top) and split the problem into smaller and smaller parts
until they became manageable. that one of the modules is the same as one used previously. so we might as well use the same module that we used last time. because Leon is not very
good at that.
 More than one person can be engaged on solving parts of the same problem
simultaneously. When each of the individual problems has been solved the
solutions are combined to produce a solution to the whole problem. but if it
is divided into:
 How is the data going to be collected from sensors and stored in the system?
 How is the decision going to be made about the changing of the lights?
 How is the data collected from the pedestrian crossing and then stored.Techniques for Writing Software. and then combined to give a
solution to the whole problem.
When a piece of software needs to be produced.
 Different people are good at different things.
Consider that you have been asked to produce a solution to the problem of computerising
a set of traffic lights in the centre of a town. Because of
this.
.
 Because the algorithms for the modules are so much shorter than for the whole
problem. However.
so he does the processing module. most
useful problems involve such complex algorithms that it is not possible to consider them
in one go. whereas he is an expert concerning controlling things using a computer.
 and processed?
 What outputs are necessary.. This
happens often.
There are other advantages in this sort of approach. because the module is quite short. The sensors used were different. software firms store the modules that they have produced so that they can be
used again if the chance arises.
These individual parts of the solution are known as modules. it is likely that the person producing a module will make fewer mistakes. so Aisha still has to produce her
module. For this reason problems are normally divided up into a number of smaller
problems. and how are they controlled?
Then each problem becomes more manageable. it is much easier to spot any errors that have
been made. however. An algorithm like
that is easy for a human being to be able think about because it is so short. our company produced a similar solution for a set of traffic lights in a
different town. each one of which can be solved separately.
This sort of approach to problem solving is called a top-down approach. The problem is a very complex one.
Also.

This type of
approach is known as a bottom up approach. then realise that we
have to provide an input module. Don’t worry about such diagrams at the moment. Although the outcome is the same it is a far
more dangerous way to approach the problem because the final outcome has not been
considered and may not be arrived at by the most efficient algorithm. and start with a control module.
If we imagine the same problem. we will meet them
again in module 3 and they will become important when we want to explain the solutions
of the major project in module 4 of this course. and so on… the problem will still be solved.One way of describing the modularisation of a problem is to use a diagram to show how
the parts fit together. although
the approach is the opposite to the one that we have just considered.
.

the solution to a problem can often be
thought of as a sequence of steps which should be taken in order. each giving a different route. the real power
of computer programs becomes apparent when we change these rules. However. There are a
number of ways of breaking out of the simple sequence.
1. one is followed if the condition is met (for instance. we will look at two of them here. The same is true when a
program is being written. the condition statement can have a number of
possible results. use a discount price
because of the number bought).
Looked at diagrammatically. and the other is followed if the condition is not met (use
the standard price). The simplest example is the command If…
Then…Else… This is used to divide the sequence into two possible routes. until you come to the end.
. this can be represented as
Start
Condition
Met
Not met
Start
Compare answer with 10
Answer >10
Answer <= 10
This example simply gives two options. by which time the problem should have been solved. There is a
condition (something like an answer being more than 10) and then two possible
outcomes. a computer program could be drawn as
Start
Program instructions
End
This type of combination of operations is known as a sequence.
Note that.
Selection
Selection is the process of making a choice. all these different routes must either come back together or must
have some suitable end point. in
order.
Diagrammatically. eventually.2. Generally.2 The structure of procedural programs
Programming Constructs
As we saw in the first section of this module. you start at the beginning and follow the steps.

Repetition
There are a number of ways of repeating the same instructions more than once.
b) The second loop structure is a WHILE…ENDWHILE loop.
Keep repeating the following commands
(LOOP)
Instructions inside loop
Until some condition is met. and the second is some method of
controlling whether the pointer is followed or whether the normal sequence of
instructions is followed.
a) The first of these loops is one where the control of the loop is at the end of the loop. This structure has the
condition at the start so that it is possible to miss out the instructions in the loop entirely.
A repeating construct is often called a loop.2. Each one of these methods have two things in
common. The first is some sort of pointer that sends control of an algorithm to some
point other than the next instruction in the sequence. We will
have a look at three methods here.
(Condition not met)
While the condition is met
Do the following commands
(Condition met)
(LOOP)
Instructions
Go back to the start of the loop
. It
is called a REPEAT…UNTIL loop.
(Condition not met) then exit loop
(condition met)
Note that the instructions in the loop have to be carried out at least once before there is
the chance of meeting the condition.

. and when it has done enough the loop is exited. or equal to.c) The third type of loop is called a FOR…NEXT loop. This loop is repeated a
predetermined number of times. the
number of times selected.
(Decide how many times to do the loop)
If the counter is less than.
do the loop again
Add 1 to
the counter
(LOOP)
Go back to the start of the loop
Note that with the For/Next loop the number of times around the loop is determined
before entry into the loop. A counter keeps check of the number of times the loop
has been done.

3. it is more likely
to look like this:
Start
Start of Module 1
Start of module 2
End of module 1
End of module 2
End
Each of the modules is called a procedure when it is in the form of a program of
instructions.
2. These small segments of program are
called procedures and functions. In
section 1. presumably. but for the sake
of clarity we will ignore them and return to our original diagram of a program:
Start
Program instructions
End
If the program has been split into sections by modularising the algorithm. When the procedure has been finished the next instruction is back where it came from
in the first place. but will return to them later. Note
two things about these procedures:
1.
. it is useful to be able to divide a problem into modules so that
each part of the problem is easier to solve.
We are not going to answer either of these questions now.2. This means that the computer must remember whereabouts it was when
it went to the procedure so that it can go back there. When the algorithm is turned into a computer
program it makes sense to program each of these smaller modules separately and then
connect them together to make the whole program. and later we’ll see what the difference is.3.Procedures and functions
As we saw in section 1. This is slightly different because the result
at the end of the procedure is a value which. they are
very similar anyway. otherwise they have been wasting their time. will be used in the main
program. and then another could be
used for reading the choice made and acting upon it.c we saw some constructs that could change the simple order. A procedure which gives a value at the end is known as a function. At some point a procedure could be
used to work out the square root of a number.
A procedure could be used for putting a menu on the screen.
runs a procedure to carry out a particular task. If they work something out. just under half way through. To start with we will call them all procedures. which itself runs another procedure. The diagram shows a main program which.
Imagine a computer program. presumably they must pass the answers back to the main
program. It is made up of a number of instructions taken in order.

So the
language which the computer uses is all in binary and very difficult for human beings to
use. are
called high-level languages. in other words. We do not need to know any more about these two translators yet. Computer
languages like this. that the person finds easy to understand. just as a letter in Chinese may need to be translated into
English if an English speaker is to be able to read it. then it has to be
translated from one to the other.
Source
code
Translator
Object
code
The object code is normally much bigger than the source code because it takes lots of
machine code commands for each of the high level language commands.
A computer can only understand 0s and 1s.
. one is called a compiler and the other is called an
interpreter. After the
source code has been translated the program is called the object code (or executable
form). the algorithm will probably be
difficult enough to follow without the language being difficult as well.
There are two types of translator. After all. If the program is written in a
high level language and the computer can only run it in machine code. binary numbers.Program Translation
When a human being writes a computer program it is important for them that they can
use a language which is easy to understand.
High-level
Language
Translator
Machine
code
A program which is written in a high level language is called the source code. Languages like this are called machine code languages. but the computer can’t.

but
3*(2+A) = X would be rejected as an error even though. a message will be
returned saying that a mistake has been made and telling the programmer which word it
cannot recognise. Logic errors. Arithmetic error.3. it is
highly unlikely that the program will produce the results that were expected. There are other ways of breaking the rules. mathematically. Another sort of logic error is sometimes referred
to as an arithmetic error. finding
where the error is can be very difficult. A good example is when a computer is asked to divide
by 0. it just
makes it produce wrong results. So X = 3*(2+A) would be
accepted by the translator. If it tells the computer to go to the wrong place.
2. Arithmetic errors are created when
inappropriate arithmetic is used. and even when the programmer realises that something has gone wrong. such a mistake does not usually make the program stop working.
3. This makes it difficult to spot that a mistake has been
made. this is impossible and would cause the program to fail. There are three types of error which can be made when program
code is being produced. This is not a difficult error
to spot because when the programmer tells the translator to translate it. These are errors in the use of the language. This is a type of logic error. If it was typed in as PLINT the translator program
would not recognise it and so would not be able to translate it. A logic error is a mistake in the way the program solution has been
designed.
Unfortunately. it is identical. Syntax errors.
A command word might be PRINT. The rules have been broken. for instance a language
might be set up to only accept a mathematical formula if it is in the form of a variable
followed by an equals sign and then a collection of variables.1.f Types of Programming Errors
When programs are being written it is not surprising that mistakes are made.
. an instruction in a program may tell the computer to jump to
another part of the program. This is fine as long as the instruction tells the computer to go
to the right part of the program.
1. For example. after all they
are very complicated.

Note that
it is produced before the system is produced.
you have a certain advantage because you know what to expect. if a program is written which uses marks out of
100 from a maths examination as input.
Think of black box as a test where you cannot see into the box (program) all you see is
what comes out at the end. If you continue the course next year. this is
the beta testing. borderline data which would be 0 and 100. Testing carried out
by the users of the program is called beta testing. Different values can be input for variables to determine whether the program can cope
with them. This involves
using a computer to solve a problem for someone. you wrote the
program. 123. These values should include typical values.
There are a number of ways of testing a program.
2. You will also get
marks if you persuade the person whose problem you are solving to test it for you. When you have written a program and you sit down to test it.Testing Methods
When a system is designed it is important that some consideration is given to making
sure that no mistakes have been made. when you take into account the different condition statements and
loops. White box testing is testing the program to determine whether all the possible paths
through the program produce the desired results.
16.. the test data would include typical data like 27. When you have finished your project
you will be expected to test whether or not it works. White box testing means that you are able to see what is
happening as the data goes through the box because it is transparent.
. Alpha and Beta testing.
73. you will have to write a project. After all.345 This type of testing is called black box testing. A schedule should be drawn up which contains a
test for every type of input that could be made and methods of testing that the program
actually does what it was meant to do.
1. For example..
3. As a large program can have a very
large number of routes. in
order to turn your AS grade into an A level. Testing carried out by people like this is known as alpha
testing. borderline values and values
which are not acceptable. this is alpha testing. This can be extended to the whole software company. This schedule is known as the test plan. and unacceptable data like –34. the company will want ordinary users to test the program because
they are likely to find errors that the software specialists did not find. as the employees are all
computer-minded people. Eventually. white box testing is rarely carried out exhaustively.

When the parts were combined they would
produce a solution to the original problem.e we were introduced to the idea of a translator
program. In section 1. This lets the programmer check to
make sure that the same variable has not been used twice for different things. A message detailing all this can be sent to the
programmer to give hints as to what to do. Either way. identifying it. This is called bottom-up programming.
the translator will know that there is something wrong.Debugging
Errors in computer solutions are called bugs. Because we are starting with a big problem
and splitting it into smaller problems. can be very
difficult and there are a number of techniques available for solving such problems. but the rules governing how it should be used have not been followed properly. as each instruction is executed. This software checks the program that has been written and finds
places where particular variables have been used. When the
program is written.b we discussed the splitting up of a problem into smaller and smaller
parts. The user works through the program
instructions manually. The dictionary tells the translator program what the rules are
for that particular special word. the errors have to be
found before they can be corrected. In this
way.
b) Traces. One is correcting
the error.3. but it still doesn’t work properly. These messages are called translator
diagnostics. these joints have to be
tested too to make sure that no silly mistakes have been made like using the same
.
1. it knows where the mistake is and.
Debugging tools are part of the software which help the user to identify where the errors
are. because the small programs have to be joined together. keeping track of the values of the variables. In section 1. They create two problems.
The technique is particularly useful for testing the finished program because it is far
easier to test a lot of small programs than it is to test one large one.3. the translator program
knows that a mistake has been made. the values can be checked to see where they suddenly change or take on an
unexpected value. Finding where the error is. The second problem. however.
c) Variable dumps.
2. this is normally fairly straightforward because most errors are caused by silly
mistakes. each small program is written separately. the translator will
not be able to find it in the dictionary and will know that something is wrong.
4. One problem can
arise. is much more complicated. At specified parts of the program. this was called top-down design. If the word
is there. Each command will have a special word which says what sort of
command it is. often. The techniques available include:
a) Cross-referencing. A trace is where the program is run and the values of all the relevant variables
are printed out. it also
knows what mistake has been made. The translator looks at the special word in the command and then goes to
its dictionary to look it up. allowing the small programs
to be tested thoroughly before being combined. Sometimes the program looks alright to the translator. until each part was a manageable size.
3. the values of all the variables are
displayed to enable the user to compare them with the expected results. Each of the commands that are in the original program are looked at separately
by the translator. Desk checking is sometimes known as a dry run. Translator diagnostics. as are the individual instructions. so it is usual to
only dry run small segments of code that the programmer suspects of harbouring an error. If the word has been typed in wrongly. Most computer
programs require a very large number of instructions to be carried out.

. and that unnecessary duplication of tests is avoided. Test strategies are important to establish before the start of testing to ensure that all the
elements of a solution are tested.variable name for two different things in two parts of the program (tested by cross
referencing).
5.

and the input is the number of marks that the student obtained in their
maths exam. For example. Help given in the code itself is known as annotation. rather than at the computer that is running it. Someone has to find the error in the program. the name is self-explanatory and hence makes the
program easier to follow.
Another way is to write comments in the code of the program which are aimed at a
human being looking at the program. The program has been fully tested and any
problems appear to have been solved.
In both these cases it is highly unlikely that the original programmer will be the person
that has to do the adapting of the code. It simply tells the
computer that anything that comes in this instruction is to be ignored.
If there is a loop structure. the variable used to store the number could be many things.
The other obvious way of making the program easier to follow is to adopt a top-down
design which enables the individual procedures to be easier to understand than one large
program.
One way to help demonstrate the structure of the program is to make parts of the
code stand out from the rest by indentation. if the
variable name X was used. However. If the original programmer had used the
variable name MATHS_MARK. the warehouse expands in order to deal with an increased supply of goods and
the computer system needs to be amended to allow enquiries from the Internet. If an input is required at some point
in the program.
. This again
implies that the program will need to be altered to accommodate the new circumstances. Some months later. perhaps a While…Endwhile loop inside the
procedure. Some
time later. Most
programming languages have an instruction that can be used for this.Annotation
Program writers need to be aware that the programs that they write will need to be
maintained long after they have gone on to other projects.
Many programming languages automatically indent some of the programming
constructs available in the language. a program is
written to control the stock in a warehouse. If this is done without some thought
then it is meaningless.
A further technique is to use sensible variable names. but if a procedure of a program is made to stand out in this
way then it is very easy to see whereabouts the procedure is. the purpose of
which is to make the code as simple as possible to follow. and an error occurs.
The new programmer is going to be grateful for all the help they can get in understanding
the old program. another programmer looking at the code would need extra
information to understand what X stood for. a particular chain of events
occurs that means that the software does some instructions in an order that has never
arisen before. then that can also be made to stand out by using a further
indent.

-When there are no more numbers to read
-The average (mean) is worked out
-The answer is then output.
1.
Note that the mark scheme is not presented in any particular algorithmic form. Also notice that the first three steps
of the algorithm are presented in two ways.5 metres high.
(4)
A. so it is highly likely that
in an exam. Either is perfectly acceptable. -Add twice x to twice y/Work out total length of walls
-Divide by . -An unknown number of numbers…
-is read into the algorithm. such a question would insist on an order as an essential feature of the
solution. provided that the two points about stating the tasks to
be carried out and specifying an order are met. One last point about the mark
scheme is that an algorithm implies that order is important.
(4)
. In other words one mark would be reserved for providing a definite
statement of order. One could be called mathematical while
the other is descriptive.Example Questions.
Set the counter to 0 and the total to 0
Read a number
Add 1 to the counter
Add the number to the total
Yes
Are there any more numbers?
No
Divide the Total by the counter
Report the answer
Describe the effect of this algorithm.
A.
A roll of wallpaper is 50cm wide.
2. Ignoring the door and any windows that
there may be. Each roll is 15m long. This
is because the syllabus does not specify that a particular form be used so it is
entirely up to the candidate.5metres/work out the number of strips of paper needed
-Divide 15metres by 2. describe an algorithm for calculating the number of rolls of wallpaper
needed to paper the room. A room measures x metres
long by y metres wide and 2.5metres/work out the number of strips in one roll of paper
-Divide number of strips needed by the number of strips in one roll
-Indication of the order required.

(2)
-.
4. and secondly that while many algorithms
are mathematically based the mathematics is not necessary to attain full marks.16. whose answer jumps from the notes.
3.
a)
A.
A piece of software is to be written which will control a central heating system.
Write down the output that the module will produce.
Notice that the arithmetic is not being tested here.Producing an algorithm to anything other than a trivial problem under exam
conditions is difficult.
b)
A.Change the WHILE X<9 DO to WHILE X<10 DO
.
Using the same structure.
E. the fact that
whatever the algorithm is it will be short. produce a similar module that will work. It is possible to get full marks
even if you can’t multiply. One solution to this problem is for the examiner to produce
the algorithm for the candidate and then expect the candidate to follow the logic.An indication that the last value used is 9 when it should have been 10.
-Handling of the input from the sensors
-Interface with the owner of the system allowing input of important values
-Processing module which makes decisions about the heating requirements
-Control of the output devices in order to carry out the processing decisions
-Alarm system in case of errors occurring.81
.
X=1
WHILE X < 9 DO
X=X+1
Y=X*X
PRINT Y
ENDWHILE
The intention of this module is to print out the square numbers from 1 to 100. no marks would be given here for saying that one is added to the counter.64. The examiner is not trying to test your mental arithmetic
but is seeing whether you can follow a small section of logic.g.
(3)
A.
-Fewer errors are likely to be made
-Any errors that are made will be easier to correct. and be careful not to simply write down what is given in the algorithm. It is
decided that the software is to be written as a set of four modules. -Many people can be involved in the solution
-Individual skills can be used
-A module can be used from the software library
-Each module is far easier to understand than the whole program is. (2)
.9.Change the X = 1 to X = 0
.36. State four
modules.
When answering a question like this pay particular attention to the number of marks
available. First.4.25.49.
5.
A standard question. whose combined solution would be a solution for the whole problem.
The example here is a very simple one but illustrates two points.
Give three advantages to using a top down approach when designing a solution to a
problem.An indication that the candidate realises that the first value of X that is used is 2
instead of 1
.
A.

These are not unique possibilities. There are plenty of other ways of achieving the
same results. The mark scheme is really one mark for correcting each of the output
errors in the original.
6.

a)
A.
b)
A.

7.

REPEAT
INPUT NUMBER
IF NUMBER <> 0 THEN TOTAL = TOTAL + NUMBER
COUNT = COUNT + 1
ELSE ZERO = ZERO + 1
UNTIL COUNT = 5
ANSWER = TOTAL/COUNT
PRINT ANSWER, ZERO
If the numbers 3,5,4,0,4,0,9,1 are used as data for this procedure, state what the
printout will be when the procedure is completed.
(2)
5 and 2. (1 mark each)
Identify the condition statement, and explain what it does.
(3)
-IF…THEN…
ELSE…
-Decides whether the number input is zero or not.
-A count is kept of all the zeros input, and the other numbers are used in the
calculation.
Note that the algorithm is provided. It would be hard to expect candidates to
produce algorithms of this type in an exam, to all but the most trivial of problems.
The description in part (b) can be in the broadest terms. The examiner is not looking
for a brilliant insight into the logic, simply for an indication that the student
understands the general principles.

State what is meant by the terms
(i) Source code
(ii) Object code
(iii) Machine code
(4)
A. -Generally, code means a set of instructions designed to carry out a task
-Source code is the version of the program written by the programmer…
- in high level language.
-Object code is the executable form of the program…
-created by the translator
-Machine code is in binary form.
Note that there are plenty of marks available here, and the fact that the mark comes
at the end of the question implies that the dotties are lumped together and that the
marks are largely interchangeable.
Teacher’s note: there is no distinction between interpreter and compiler as yet. Even
to the extent that students are not penalised for not knowing that the interpreter does
not produce an object code. It is not yet in the syllabus, so should not be expected.

8.

Describe the relationship between the source code and the object code.

(2)
A. -The source code is the original program while the object code is after translation.
- There is a one to many relationship between the two.
Note. This could have been a very complex answer. However, you don’t know a lot
about translators and their effects yet, and a look at the number of marks available
tells you that the answer is strictly limited. The second mark point is rather
strangely put, it simply means that the object code is longer than the source code,
and if that’s what you said you would get the mark.
9.

State three types of program error and give an example of each.
(6)
-Syntax error
-Mistyping a reserved word, eg typing plint instead of print
-Logic error
-A jump instruction that tells the computer to jump to the wrong place
-Arithmetic error
-Inappropriate use of arithmetic. Eg dividing by zero
Note. There are many possible errors that could be given as examples of each of
these. It is sensible to stick to the standard answers that way there is no chance of
picking a wrong one.

10.

A program is written that will allow the user to input a list of 5 numbers and will
print out the largest and the smallest of them.
The program is to be tested to see that it works under all conditions. The
programmer decides to use the test data 3,4,2,5,6,7 in order to test what will happen
if more than 5 numbers are input.
Give four other different sets of test data explaining the purpose of each.
(8)
A. - 1,3,-4,6,5
-To determine how it handles negative numbers.
- 1,3,4,-6,5
-To determine whether it chooses the largest number according to magnitude or
whether it takes the sign into consideration.
- 1.5,3,4,5,6
- To determine whether it can deal with fractions.
- 1,1,1,1,1
-To see what happens if the largest and the smallest are the same.
Note. There are many more sensible sets of test data that could be used. These are
just examples. Make sure that you read the question carefully and give ‘different’
sets of test data. Just changing the data doesn’t make it different, it is the reason for
the choice of data that must be different.

11. Explain the difference between alpha testing and beta testing. (2)
A. -Alpha testing is done by the programmer or in the software house.
-Beta testing is done by the user.

12.

Explain how the translator program can issue error diagnostics and give an example
of an error that can be spotted by the translator.
(3)
A. - Translator compares reserved word/syntax (rules) in its dictionary
- If different to what is in the dictionary the user can be told what and where the
error is.
-eg PLINT is not in the dictionary of words that it knows, so there must be an error.
Note. The same example has been used again. I know this one is right, why risk
changing it?

13.

Bugs are common in computer programs. Describe two techniques that can be used
to help debug a program.
(4)
A. - Cross referencing of variables
- checks the program for occurences of the same variable being used more than
once.
- Trace table.
- As the program is run the values of the variables are printed out as the instructions
are executed, allowing the user to see where sudden, unexpected, changes have
occurred.
Note. There are lots of possible answers here, always choose the two answers that
you are absolutely sure of.

14.a)Describe what is meant by annotation of a program code.
(2)
A. -Explanation of the techniques used in the algorithm
-Needed by people employed to maintain or amend the program in the future…
-by explaining the logic and the reasoning behind the code.
b) Describe two methods that can be used to annotate code.
(4)
-Indentation of groups of statements.
-This not only makes the group stand out, but also ensures that the person looking at
the code knows which statements should be treated together.
- Use of sensible variable names.
-This means that long references to look up tables are not needed and helps to make
the understanding of lines of instruction easier to follow.
Note. Again, these are standard answers, but no less effective for that and safe
because we know they are going to be right.

System Design: Input, Output, User Interface

Output Design
Output is the primary purpose of any system.
These guidelines apply for the most part to both paper and screen
outputs. Output design is often discussed before other aspects of design
because, from the client's point of view, the output is the system.

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Problems often associated with business information output are
information delay.
excessive distribution. It is more compact than
traditional output and may be produced as fast as non-impact
printer output. high speed.
An information clearinghouse (or information center) is a service
center that provides consultation.
Page decoupling is the separation of pages into cohesive groups.
Output may be designed to aid future change by stressing
unstructured reports. Inputs. and leaving room on summary
reports for added ratios and statistics.Output is what the client is buying when he or she pays for a
development project.
Report requirements documents contain general report
information and field specifications. databases. and (2) turn action documents into turnaround
documents. information (data) overload.
Turnaround documents reduce the cost of internal information
processing by reducing both data entry and associated errors.
Fields on a report should be selected carefully to provide
uncluttered reports.
An output intermediary can restrict access to key information and
prevent unauthorized access. and
reduce information (data) overload. paper domination. and nontailoring. facilitate 80-column remote printing.
People often receive reports they do not need because the
number of reports received is perceived as a measure of power. fields for control
breaks. and exception fields. located in the data
center Remote site printers: medium speed.
Periodic reports have set frequencies such as daily or weekly.
Two ways to design output for strategic purposes are (1) make it
compatible with processes outside the immediate scope of the
system.
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Mainframe printers: high volume. making
field constants into variables. close to end user. and documentation
to encourage end-user development and use of applications. fields that change.
Page breaks and control breaks allow for summary totals on key
fields. defining field size for future growth.
Detail and summary reports differ in the the former support dayto-day operation of the business while the latter include statistics
and ratios used by managers to assess the health of operations. print layout sheets present a
picture of what the report will actually look like. and processes exist to provide
output.
The specifications needed to describe the output of a system are:
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The types of fields which should be considered for business
output are: key fields for access to information. ad
hoc reports are produced at irregular intervals. assistance.
COM is Computer Output Microfilm.
Output can now be more easily tailored to the needs of individual
users because inquiry-based systems allow users themselves to
create ad hoc reports.

mnemonic coding represents data in a form
that is easier for the user to understand and remember.g.
Input Design
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A source document differs from a turnaround document in that
the former contains data that change the status of a resource
while the latter is a machine readable document.
Periodic Reports: produced with a set frequency (daily.
Numeric coding substitutes numbers for character data (e. weekly.)
Ad-Hoc (On Demand) Reports: irregular interval.
stock paper. not as "pretty".
M=male. problems.
A document should be concise because longer documents contain
more data and so take longer to enter and have a greater chance
of data entry errors.
Internal Reports: for use within the organization.. etc.
monthly. data structure
specifications.
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..data flow diagrams. produced upon
user demand.g. 2=female).
often on preprinted forms.
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Transaction throughput is the number of error-free
transactions entered during a specified time period.
Exception Reports: only shows errors. data flow specifications. and data element specifications.
Output Documents
Printed Reports
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External Reports: for use or distribution outside the organization. out-of-range
values. greenbar. etc. (e. every fifth Tuesday. F=female).
Detail Reports: one line per transaction.
Summary Reports: an overview.
1=male. or unexpected conditions or events.

An example of an illogical combination in a payroll system would
be an option to eliminate federal tax withholding."
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Be user-centric and attempt to convey to the user that he or she
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An error suspense record would include the following fields: data
entry operator identification. Possibly even to the point of
avoiding pejorative terms such as "invalid" "illegal" or "bad.
(BAD: Syntax error. Shneiderman means allowing
the user to obtain more detailed explanations of an error by using
a help option. not general. or vague.
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Be positive. date transaction reentered successfully. Invalid entry.
By "multiple levels" of messages.
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The more quickly an error is detected. transaction image. transaction type. transaction entry date..Be constructive. but not forcing a lengthy message on a user who
does not want it.e. Avoid condemnation. type and length). General Failure)
Don't JUST say what's wrong---. ambiguous. suggest what
needs to be done to correct the error condition. transaction
entry time. fields in error.
error codes.
Error Messages to be displayed for the end user
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Be specific and precise. the closer the error is to
the person who generated it and so the error is more easily
corrected.
A data input specification is a detailed description of the
individual fields (data elements) on an input document together
with their characteristics (i.

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is in control by replacing imperatives such as "Enter date" with
wording such as "Ready for date.from a particular screen or the
application
1.
Consistency in terminology and wording.further delineate choice of
functions
5. Help screens -.)
Interactive Screen Design
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The primary differences between
an interactive and batch environment are:
o interactive processing is done during the organization's
prime work hours
o interactive systems usually have multiple.how to perform a task
7.
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The seven step path that marks the structure of an interactive
system is
Greeting screen (e."
Consider multiple message levels: the initial or default error
message can be brief but allow the user some mechanism to
request additional information.
o place error messages in the same place on the screen
o use consistent display characteristics (blinking.
2.. simultaneous
users
o the experience level of users runs from novice to highly
experienced
o developers must be good communicators because of the
need to design systems with error messages. color.g. Function screens -.
beeping.
and requests for user responses.
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The difference between inquiry and command language dialogue
modes is that the former asks the user to provide a response to a simple
.updating or deleting records
6.to prevent unauthorized use
Main menu -. help text.
3. company logo)
Password screen -. etc.allow choice of several available applications
Intermediate menus -.
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An intermediate menu and a function screen differ in that the
former provides choices from a set of related operations while the latter
provides the ability to perform tasks such as updates or deletes. Escape options -.
4.

high priority
messages... For example. Escape option
7. At one time "312" was a default value for Area Code.
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Directions for designing form-filling screens:
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Fields on the screen should be in the same sequence as on
the source document. User instructions
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Edit all entered fields for transaction errors.
.g.
Move the cursor automatically to the next entry field
Allow entry to be free-form (e. or items that must be changed. 773. Menu list
6.what application the user is currently in
2. Locator -.allows the more experienced user access
without going through the entire menu tree.g. Unix shell prompt). 847)
providing a default value for this field is no longer as useful. Menu ID -. VAX/VMS $ prompt.. 630. User response area
8. but with
the additional Area Codes now in use (312.
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The eight parts of an interactive screen menu are:
1.g.. GUI Interface
(Windows. Macintosh) provide Dialog Boxes to prompt user to input
required information/parameters.question (e. System messages (e. MSDOS C:> prompt. Title
4. unusual values.
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Potential problems associated with the overuse of color are:
o
Colors have different meanings to different people and in
different cultures.g. at SXU the
screen on which student names and addresses are entered has a default
value of "IL" for State since the majority of students have addresses in
Illinois.
Use cuing to provide the user with information such as
field formats (e.g. "Do you really want to delete this file?") where the latter
requires that the user know what he or she wants to do next (e. error messages)
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Highlighting should be used for gaining attention and so should
be limited to critical information. dates)
Provide default values. do not make the user
enter leading zeroes)
Consider having all entries made at the same position on
the screen. 708..
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A default value is a value automatically supplied by the
application when the user leaves a field blank.

Separate text paragraphs with at least one blank line. fatigue.
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Rules
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for defining message content include:
Use active voice.
Use mixed case (upper and lower case) letters. environmental conditions.
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Symmetry is important to screen design because it is
aesthetically pleasing and thus more comforting.
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Input verification is asking the user to confirm his or her most
recent input (e.
boredom.
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The elements of the adaptive model are:
o Triggering question to determine user experience level
o Differentiation among user experience
o Alternative processing paths based on user level
o Transition of casual user to experienced processing path
o Transition of novice user to experienced processing path
o Allowing the user to move to an easier processing path
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Interactive tasks can be designed for closure by providing the
user with feedback indicating that a task has been completed.
Do not patronize.o
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A certain percentage of the population is known to have
color vision deficiency. simple sentences. "Are you sure you want to delete this file?")
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Adaptive models are useful because they adapt to the user's
experience level as he or she moves from novice to experienced over
time as experience with the system grows.
Use short.
Some color combinations may be disruptive.g.
Avoid hyphenation and unnecessary punctuation.
Use humor carefully.
Avoid word contractions and abbreviations..
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Information density is important because density that is too high
makes it more difficult to discern the information presented on a screen.
Keep field width within 40 characters for easy reading.
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Internal locus of control is making users feel that they are in
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Avoid godlike language.
Use nonthreatening language.
Use affirmative statements.
especially for novice users.
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"Within User" sources of variation include: warm up. and extraneous events.

control of the system. function
keys. rather than that the system is in control of them.
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Some common user shortcuts are: direct menu access. and shortened response time.
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Examples of distracting use of surprise are:
o Highlighting
o Input verification
o Flashing messages
o Auditory messages
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Losing the interactive user can be avoided by using short menu
paths and "You are here" prompts.
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